vimscriptfull.xml

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<GUIDE title="Google Vimscript Guide">
  <p class="revision">

    Revision 1.1
  </p>

  
  <address>
    Nate Soares<br/>
    Joshua Hoak<br/>
    David Barnett<br/>
  </address>

  <OVERVIEW>
    <CATEGORY title="Background">
      <p>
        This is the in-depth vimscript guide. If you're just a casual user
        looking to write a plugin, the
        <a href="vimscriptguide.html">abbreviated style guide</a> is for you.
      </p>
      <p>
        This rather rotund guide dives into justifications and clarifications.
        It provides an idealized set of rules that are rather too draconian to
        push on casual scripters.
      </p>
      
      <p>
        It's for users who want to know why certain decisions were made in the
        abbreviated guide and who want to learn a thing or two about using
        vimscript safely.
      </p>
      <p>
        Fair warning: Vimscript is a maddening abyss. When you gaze into it, it
        gazes also into you. Proceed with caution.
      </p>
    </CATEGORY>
  </OVERVIEW>

  <CATEGORY title="Portability">
    <p>
      Vim is highly configurable. Users can change many of the default
      settings, including the case sensitivity, the regular expression rules,
      the substitution rules, and more. In order for your vimscript to work
      for all users, follow these guidelines:
    </p>
    <ul>
      <li>
        Always prefix regular expressions with one of <code>\m</code>,
        <code>\v</code>, <code>\M</code>, or <code>\V</code> (prefer
        tersity)
        <ul>
          <li>
            Users can change the global "magic level" of regular expressions.
            This changes how atoms are parsed in regular expressions,
            including <code>.</code>, <code>*</code>, and <code>{</code>.
          </li>
          <li>
            Even if your regular expression does not contain characters which
            are affected by the <code>magic</code> setting you must prefix it
            with one of the magic control atoms. This future-proofs your
            regular expression against other devs modifying it and forgetting
            to add the control atom.
          </li>
          <li>
            If you have no opinion about what type of regular expression to
            use, prefer the one which makes your regular expression most
            concise.
          </li>
        </ul>
      </li>
      <li>
        Avoid using <code>:s[ubstitute]</code> in scripts.
        <ul>
          <li>
            <code>:substitute</code> moves the cursor.
          </li>
          <li>
            <code>:substitute</code> outputs an error message when the match
            does not exist.
          </li>
          <li>
            The meaning of the <code>g</code> flag depends upon the
            <code>gdefault</code> setting. If you do use
            <code>:substitute</code> you must save <code>gdefault</code>, set
            it to <code>0</code> or <code>1</code>, perform the substitution,
            and then restore it.
          </li>
          <li>
            Script authors who want a safe way to replace text in the buffer
            are encouraged to use <code>maktaba#buffer#Replace</code>.
          </li>
        </ul>
      </li>
      <li>
        Always use case-explicit operators for strings (<code>=~#</code> and
        <code>=~?</code>, never <code>=~</code>).
        <ul>
          <li>
            This also applies to <code>!~ == != &gt; &gt;= &lt;</code> and
            <code>&lt;=</code>
          </li>
          <li>
            This only applies for strings. <code>==</code> and
            <code>&gt;=</code> are fine for numbers, but <code>==#</code> and
            <code>&gt;=#</code> must be used for strings.
          </li>
          <li>
            The behavior of <code>=~</code> and friends is dependant upon the
            <code>ignorecase</code> setting.
          </li>
          <li>
            You may break this rule when you explicitly want to obey the
            user's <code>ignorecase</code> setting. Be prepared to justify
            your reasoning.
          </li>
        </ul>
      </li>
      <li>
        When using regular expressions as arguments to functions, prepend them
        with <code>\c</code> or <code>\C</code>.
        <ul>
          <li>
            This forces case to be either explicitly matched or ignored.
          </li>
          <li>
            This is recommended, but not required, when comparing regexes with
            operators that specify case sensitivity (<code>=~#</code>, etc.).
          </li>
          <li>
            This rule applies when your regexes are matching syntax, external
            APIs, external messages, and most other cases.
          </li>
          <li>
            It does not apply when matching text in the buffer. When matching
            text in the buffer you should honor the <code>ignorecase</code>
            setting.
          </li>
          <li>
            You may also ignore this rule any time that you explicitly want to
            honor the <code>ignorecase</code> setting. Be prepared to justify
            your reasoning.
          </li>
        </ul>
      </li>
      <li>
        Always use <code>normal!</code> instead of <code>normal</code>.
        <ul>
          <li>
            If you forgo the <code>!</code> the command will use the user's
            key mappings and you have literally no idea what your macro will
            do.
          </li>
        </ul>
      </li>
      <li>
        Always use the <code>noremap</code> family of commands.
        <ul>
          <li>
            Your plugins generally shouldn't introduce mappings, but if they
            do, the <code>map</code> command respects the users existing
            mappings and could do anything.
          </li>
        </ul>
      </li>
      <li>
        When using <code>catch</code>, match the error code rather than the
        error text.
        <ul>
          <li>
            The error text may be locale-dependant.
          </li>
          <li>
            See <code>:help error-messages</code>.
          </li>
        </ul>
      </li>
    </ul>
    <p>
      In general, guard all commands and functions against user settings.
    </p>
    
  </CATEGORY>
  <CATEGORY title="Language Guide">
    <ul>
      
      
      <li>
        Line continuations: <strong>Yes</strong>
        <ul>
          
          <li>
            Plugins that support vi compatibility mode must save and restore
            compatibility options as described in the
            <strong>Errata section</strong> so line continuations work properly.
          </li>
        </ul>
      </li>
      <li>
        Exceptions: <strong>Yes, with caution</strong>
        <ul>
          <li>
            Always use an error code in thrown exception messages.
          </li>
          <li>
            Prefer the <code>maktaba#error</code> codes found in
            <code>maktaba</code>.
          </li>
          <li>
            Fall back to the vim error codes. See
            <code>:help error-messages</code>.
          </li>
          <li>
            Generate custom error messages using
            <code>maktaba#error#Message</code>.
          </li>
        </ul>
      </li>
      <li>
        Global Variables: <strong>As configuration only</strong>
        <ul>
          <li>
            See the plugin guide.
          </li>
        </ul>
      </li>
      <li>
        Messaging: <strong>As little as possible.</strong>
        <ul>
          <li>
            Loud scripts are annoying.
          </li>
          <li>
            Message the user when an error has occured.
          </li>
          <li>
            Message the user when an operation which takes a long time has
            begun work.
          </li>
          <li>
            Avoid messaging otherwise.
          </li>
        </ul>
      </li>
      <li>
        Type checking:
        <strong>Use strict and explicit checks where possible.</strong>
        <ul>
          <li>
            Vimscript has unsafe, unintuitive behavior when dealing with some
            types. For instance, <code>0 == 'foo'</code> evaluates to true.
          </li>
          <li>
            Use strict comparison operators where possible. When comparing
            against a string literal, use the <code>is#</code> operator.
            Otherwise, prefer <code>maktaba#value#IsEqual</code> or check
            <code>type()</code> explicitly.
          </li>
          <li>
            Check variable types explicitly before using them. Use functions
            from <code>maktaba#ensure</code>, or check
            <code>maktaba#value</code> or <code>type()</code> and throw your own
            errors.
          </li>
          <li>
            Use <code>:unlet</code> for variables that may change types,
            particularly those assigned inside loops.
          </li>
        </ul>
      </li>
      <li>
        FuncRefs: <strong>No in most cases.</strong>
        <ul>
          <li>
            FuncRefs have inconsistently enforced naming restrictions.
            (Functions can have names that FuncRefs can not.)
          </li>
          <li>
            FuncRefs have inconsistent ability to be reassigned (in Vim
            7.2 and before you must unlet a FuncRef before assigning it).
          </li>
          <li>
            In most instances where a FuncRef is needed a string works
            just as well: just pass the string that you would use to make
            the FuncRef.
          </li>
          <li>
            Consider using <code>maktaba#function</code> instead to create and
            manipulate handles to functions.
          </li>
        </ul>
      </li>
      <li>
        Python: <strong>Sparingly</strong>
        <ul>
          
          <li>
            Hurts code reuse since python code embedded in python plugins is
            awkward to share between plugins.
          </li>
          <li>
            Using python introduces python language version dependencies, which
            are likely to get stale.
          </li>
          <li>
            Exception: It's reasonable to use python for plugin functionality
            that needs to do work in the background, as vimscript can not do
            this.
          </li>
        </ul>
      </li>
      <li>
        Ruby: <strong>No</strong>
        <ul>
          <li>
            We can not assume ruby interoperability.
          </li>
          <li>
            You shouldn't depend upon the version of the ruby language that the
            user has installed.
          </li>
        </ul>
      </li>
      <li>
        Lua: <strong>No</strong>
        <ul>
          <li>
            For the same reasons an Ruby.
          </li>
        </ul>
      </li>
      <li>
        Dict Functions: <strong>Encouraged</strong>
        <ul>
          <li>
            Vimscript can attach functions to dictionaries. Such functions
            have access to the <code>self</code> parameter which access
            the dict state.
          </li>
          <li>
            Use these where you would use a class in python.
          </li>
          <li>
            Do not over-use this feature; it is not necessary for helper
            functions or API functions, only for encapsulated objects.
          </li>
        </ul>
      </li>
    </ul>
    <p>
      All other language features are fair game.
    </p>
  </CATEGORY>
  <CATEGORY title="Structure">
    <ul>
      <li>
        Provided functionality should be packed into modular plugins.
        <ul>
          <li>
            Every function in your plugin should be specific to your
            plugin.
          </li>
          <li>
            General utility functions should be abstracted into library plugins.
          </li>
          <li>
            Manage dependencies with <code>maktaba</code>.
          </li>
        </ul>
      </li>
      <li>
        <code>plugin-names-like-this</code>
        <ul>
          <li>
            Plugin names should be descriptive and concise.
          </li>
          
          
        </ul>
      </li>
      <li>
        Each plugin must consist of one directory (or code repository), sharing
        a name with the plugin (with a "vim-" prefix or ".vim" suffix if
        desired).
      </li>
      <li>
        Plugin metadata should be declared in the addon-info.json format (see
        the <a href="http://goo.gl/CUXJZC">VAM documentation</a> for details).
      </li>
      <li>
        Functions should go in the <code>autoload/</code> subdirectory of
        your plugin.
        <ul>
          <li>
            This allows them to be late-loaded, which speeds up startup
            time.
          </li>
          <li>
            This helps vim enforce namespacing conventions.
          </li>
        </ul>
      </li>
      <li>
        Each file in the <code>plugin/</code> or <code>instant/</code> directory
        should begin with the boilerplate
        <CODE_SNIPPET>
          let [s:plugin, s:enter] = maktaba#plugin#Enter(expand('&lt;sfile&gt;:p'))
          if !s:enter
            finish
          endif
        </CODE_SNIPPET>
        (This prevents re-entry and allows users to selectively disable
        functionality.)
      </li>
      <li>
        User configuration should be via plugin flags defined in
        <code>instant/flags.vim</code>.
        <ul>
          <li>
            Define flags with
            <code>call s:plugin.Flag('FLAGNAME', DEFAULT_VALUE)</code>.
          </li>
          <li>
            Users can configure these flags using the <code>:Glaive</code>
            command (see <a href="https://github.com/google/glaive">glaive</a>).
          </li>
        </ul>
      </li>
      <li>
        Commands, autocommands, mappings, and settings changes should
        occur either in the <code>plugin/</code> or the
        <code>ftplugin/</code> subdirectories.
        <ul>
          <li>
            All commands should be defined in <code>plugin/commands.vim</code>
            or <code>ftplugin/</code> files.
          </li>
          <li>
            Autocommands should be defined in <code>plugin/autocmds.vim</code>,
            inside an augroup.
          </li>
          <li>
            Mappings should be defined in <code>plugin/mappings.vim</code> and
            will be disabled unless explicitly enabled by users.
          </li>
          <li>
            If the plugin configures any standard vim settings, those should be
            configured in <code>plugin/settings.vim</code> or
            <code>instant/settings.vim</code>.
          </li>
        </ul>
      </li>
      <li>
        Avoid using the <code>after/</code> subdirectory.
        <ul>
          <li>
            <code>after/</code> should be reserved for the user.
          </li>
          <li>
            It is difficult for the user to add their own overrides when
            plugins use <code>after/</code>.
          </li>
        </ul>
      </li>
    </ul>

    <STYLEPOINT title="Libraries vs. Functionality">
      <SUMMARY>
        Separate library-providing plugins from command-providing plugins.
      </SUMMARY>
      <BODY>
        <p>
          Many plugins provide either user functionality (commands,
          autocommands, etc) or an API (of autoloaded functions) but not both.
          This separation is encouraged, as it allows other plugins to pull in a
          library without also pulling in commands, setting changes, and other
          plugin functionality that affects the end user.
        </p>
      </BODY>
    </STYLEPOINT>

    <STYLEPOINT title="Configuration">
      <SUMMARY>
        Don't clobber user settings. Provide as much configurability as
        possible: that's what Vim's all about.
      </SUMMARY>
      <BODY>
        <ul>
          <li>
            Use maktaba flags for plugin configuration. Users can configure them
            using the <code>:Glaive</code> command.
            
          </li>
          <li>
            Check if configuration variables exist before setting them.
            <CODE_SNIPPET>
              if !exists('g:myplugin_option')
                let g:myplugin_option = 1
              endif
            </CODE_SNIPPET>
          </li>
        </ul>
      </BODY>
    </STYLEPOINT>
  </CATEGORY>
  <CATEGORY title="Style Guide">
    <p>
      Follow google-wide style conventions. Mimic google python style when
      in doubt.
    </p>

    

    <STYLEPOINT title="Documentation">
      <SUMMARY>
        Use <a href="https://github.com/google/vimdoc">vimdoc</a>.
      </SUMMARY>
      <BODY>
        <p>
          Provide help files generated by
          <a href="https://github.com/google/vimdoc">vimdoc</a>. Write
          documentation in .vim files in conformance with the vimdoc standards
          and include fields like "description" and "author" in the
          addon-info.json file (see the
          <a href="http://goo.gl/CUXJZC">VAM documentation</a>).
        </p>
      </BODY>
    </STYLEPOINT>

    <STYLEPOINT title="Whitespace">
      <SUMMARY>
        Follow google-wide conventions.
      </SUMMARY>
      <BODY>
        <ul>
          <li>
            Use two spaces for indents.
          </li>
          <li>
            Do not use tabs.
          </li>
          <li>
            Use spaces around operators except for arguments to commands.
            <ul>
              <li>
                Using spaces around operators for commands is often invalid
                syntax. This is inconsistently enforced by vimscript. To be
                safe, always omit whitespace around arguments to commands.
              </li>
              <li>
                <CODE_SNIPPET>
                  let s:variable = "concatenated " . "strings"
                  command -range=% MyCommand
                </CODE_SNIPPET>
                <BAD_CODE_SNIPPET>
                  let s:variable="concatenated "."strings"
                  command -range = % MyCommand
                </BAD_CODE_SNIPPET>
              </li>
            </ul>
          </li>
          <li>
            Do not introduce trailing whitespace.
            <ul>
              <li>
                You need not go out of your way to remove it.
              </li>
            </ul>
          </li>
          <li>
            Restrict lines to 80 columns wide.
          </li>
          <li>
            Indent continued lines by two tabs (four spaces).
          </li>
          <li>
            Do not waste whitespace aligning common segments of similar
            commands. It is both difficult and expensive to maintain.
            <ul>
              <li>
                <CODE_SNIPPET>
                  command -bang MyCommand call myplugin#foo()
                  command MyCommand2 call myplugin#bar()
                </CODE_SNIPPET>
                <BAD_CODE_SNIPPET>
                  command -bang MyCommand  call myplugin#foo()
                  command       MyCommand2 call myplugin#bar()
                </BAD_CODE_SNIPPET>
              </li>
            </ul>
          </li>
        </ul>
        <SUBSECTION title="Line Continuations">
          <ul start="7">
            <li>
              Prefer line continuations on semantic boundaries.
              <ul>
                <li>
                  <CODE_SNIPPET>
                    command SomeLongCommand
                        \ call some#function()
                  </CODE_SNIPPET>
                  <BAD_CODE_SNIPPET>
                    command SomeLongCommand call
                        \ some#function()
                  </BAD_CODE_SNIPPET>
                </li>
                <li>
                  Use your best judgement.
                </li>
              </ul>
            </li>
            <li>
              Place one space after the backslash denoting a line continuation.
              <ul>
                <li>
                  When continuing a multi-line command a pipe can be substituted
                  for this space as necessary, as follows:
                  <CODE_SNIPPET>
                    autocommand BufEnter &lt;buffer&gt;
                        \ if !empty(s:var)
                        \|  call some#function()
                        \|else
                        \|  call some#function(s:var)
                        \|endif
                  </CODE_SNIPPET>
                </li>
              </ul>
            </li>
            <li>
              Do not continue multi-line commands when you can avoid it. Prefer
              function calls.
            </li>
          </ul>
        </SUBSECTION>
        <SUBSECTION title="Comments">
          <ul>
            <li>
              Place a space after the <code>"</code> before the comment text.
              <ul>
                <li>
                  <CODE_SNIPPET>
                    " I am a line comment.
                    call call(s:my_function)
                  </CODE_SNIPPET>
                </li>
              </ul>
            </li>
            <li>
              Do not use inline comments.
              <ul>
                <li>
                  Some commands treat them as comments and others as unclosed
                  quotes.  There are many edge cases. It's difficult to get
                  right and difficult to maintain.
                </li>
                <li>
                  Where you would use an inline comment, put a line comment on
                  the line above.
                </li>
              </ul>
            </li>
            <li>
              When leaving blank lines in comments, include the quote in the
              blank line.
              <ul>
                <li>
                  <CODE_SNIPPET>
                    " I am one continuous
                    "
                    " comment block
                  </CODE_SNIPPET>
                </li>
              </ul>
            </li>
          </ul>
        </SUBSECTION>
      </BODY>
    </STYLEPOINT>

    <STYLEPOINT title="Variables">
      <SUMMARY>
        <p>
          <code>plugin-names-like-this</code>,
          <code>FunctionNamesLikeThis</code>,
          <code>CommandNamesLikeThis</code>,
          <code>augroup_names_like_this</code>,
          <code>variable_names_like_this</code>.
        </p>
        <p>
          Prefix all variables with their scope.
        </p>
      </SUMMARY>
      <BODY>
        <ul>
          <li>
            <code>variable_names_like_this</code>
            <ul>
              <li>
                FuncRef variables count as functions and should be named like
                functions.
              </li>
              <li>
                This (pathological) convention is enforced by vim itself.
              </li>
            </ul>
          </li>
          <li>
            Prefix global variables with <code>g:</code>
            <ul>
              <li>
                Vimscript allows you to create global variables without
                prefixing them.
              </li>
              <li>
                It is very bad practice to introduce non-prefixed global
                variables into scope.
              </li>
              <li>
                Global variables should only be used for plugin configuration.
              </li>
              <li>
                This does not apply to functions defined in
                <code>autoload</code> directories.
              </li>
            </ul>
          </li>
          <li>
            Prefix script-local variables with <code>s:</code>
            <ul>
              <li>
                This prevents namespace collisions between plugins.
              </li>
              <li>
                This also applies to script-local functions.
              </li>
            </ul>
          </li>
          <li>
            Prefix function arguments with <code>a:</code>
            <ul>
              <li>
                This is enforced by vim itself.
              </li>
            </ul>
          </li>
          <li>
            Prefix function-local variables with <code>l:</code>
            <ul>
              <li>
                This is not enforced by vimscript but is good practice.
              </li>
              <li>
                It helps you remember that all other variables must be
                prefixed with scope.
              </li>
              <li>
                <code>l:</code> disambiguates between function-local and
                vim-predefined variables. For example, <code>count</code>
                refers to
                <code>v:count</code>, not <code>l:count</code>.
              </li>
              <li>
                It future proofs your scripts against the introduction of new
                vim-predefined variables.
              </li>
            </ul>
          </li>
          <li>
            Prefix pre-defined vim variables with <code>v:</code>
            <ul>
              <li>
                This is not enforced by vimscript but is good practice.
              </li>
              <li>
                It provides context as to where the (undeclared) variable is
                coming from.
              </li>
              <li>
                It reminds you that the variable can not be assigned to.
              </li>
            </ul>
          </li>
          <li>
            Prefix buffer-local variables with <code>b:</code>
            <ul>
              <li>
                This is useful for plugins that keep per-buffer state.
              </li>
            </ul>
          </li>
        </ul>
      </BODY>
    </STYLEPOINT>

    <STYLEPOINT title="Strings">
      <SUMMARY>
        Prefer single quotes.
      </SUMMARY>
      <BODY>
        <p>
          Prefer single quoted strings. Specifically, in order of precedence:
        </p>
        <ul>
          <li>
            Always use single quotes for regular expressions.
            <ul>
              <li>
                <code>'\s*'</code> is not the same as <code>"\s*"</code>
              </li>
              <li>
                Single quotes will prevent the need for excessive backslashes.
              </li>
              <li>
                Double single quotes escape to one single quote in single
                quoted strings: <code>'example ('')'</code> represents the
                string
                <code>example (')</code>
              </li>
            </ul>
          </li>
          <li>
            If your string requires escape characters (<code>\n</code>,
            <code>\t</code>, etc.) use double quotes.
            <ul>
              <li>
                Escapes can not be expressed in single quoted strings.
              </li>
              <li>
                Remember that <code>'\n'</code> in a regex does not represent a
                newline, but rather "\n". You only need to use double quotes
                when you want to embed the represented character itself (e.g. a
                newline) in the string.
              </li>
            </ul>
          </li>
          <li>
            If your string contains no escapes nor single quotes, use single
            quoted strings.
            <ul>
              <li>
                Most strings in vimscript are regexes, so this provides maximum
                consistency.
              </li>
            </ul>
          </li>
          <li>
            If your non-regex string contains single quotes but no double
            quotes, use double quotes.
            <ul>
              <li>
                Don't bother escaping strings if you don't have to.
              </li>
              <li>
                This is similar to the python string rules.
              </li>
            </ul>
          </li>
          <li>
            If your string contains both single and double quotes, use whichever
            quoting style requires less escaping.
            <ul>
              <li>
                Break ties in favor of single quotes.
              </li>
            </ul>
          </li>
        </ul>
      </BODY>
    </STYLEPOINT>

    <STYLEPOINT title="Settings">
      <SUMMARY>
        Prefer long names. Set settings locally.
      </SUMMARY>
      <BODY>
        <ul start="6">
          <li>
            Prefer long names of built in settings (i.e. <code>tabstop</code>
            over
            <code>ts</code>).
          </li>
          <li>
            Set local settings unless you explicitly want to set global
            settings.
            <ul>
              <li>
                Use <code>setlocal</code> and <code>&amp;l:</code> instead of
                <code>set</code> and <code>&amp;</code>.
              </li>
            </ul>
          </li>
        </ul>
      </BODY>
    </STYLEPOINT>
  </CATEGORY>
  <CATEGORY title="Usage Guide">
    <p>
      Vim plugins should provide any or all of the following:
      <strong>Commands,</strong> <strong>Autocommands,</strong>
      <strong>Functions,</strong> <strong>Statusline Flags, and</strong>
      <strong>Mappings.</strong>
    </p>

    <STYLEPOINT title="Commands">
      <SUMMARY>
        <ul>
          <li>Define in <code>plugin/commands.vim</code>.</li>
          <li>CommandNamesLikeThis.</li>
          <li>Prefer semantic names to a unified prefix.</li>
          <li>Do not use <code>[!]</code></li>
          <li>Extract logic into functions.</li>
        </ul>
      </SUMMARY>
      <BODY>
        <ul>
          <li>
            <code>CommandNamesLikeThis</code>
          </li>
          <li>
            Commands should be defined in one block with no whitespace between
            them.
            <ul>
              <li>
                Name commands semantically at the expense of a common prefix.
              </li>
              <li>
                <BAD_CODE_SNIPPET>
                  command WhitespaceFixTrailing
                  command WhitespaceFixIndentation
                </BAD_CODE_SNIPPET>
                <CODE_SNIPPET>
                  command FixTrailingWhitespace
                  command FixIndentation
                </CODE_SNIPPET>
              </li>
            </ul>
          </li>
          <li>
            Use <code>command</code> without a bang.
            <ul>
              <li>
                This notifies users to command name conflicts immediately at
                startup.
              </li>
              <li>
                Command name collisions are an error and should not fail
                silently.
              </li>
              <li>
                Plugins are guarded against re-entry, so a single vim session
                should never attempt to re-define defined commands.
              </li>
            </ul>
          </li>
          <li>
            Do not put logic in commands.
            <ul>
              <li>
                Delegate to functions instead.
              </li>
              <li>
                Pass non-argument command parameters (<code>&lt;bang&gt;</code>,
                <code>&lt;register&gt;</code>, etc.) before argument parameters
                (<code>&lt;f-args&gt;</code>, etc.).
              </li>
              <li>
                Otherwise variable-length argument functions are difficult to
                implement.
              </li>
            </ul>
          </li>
          <li>
            Do not autoload commands.
            <ul>
              <li>
                Autoloaded commands will not be available until after a function
                in the same file is called.
              </li>
              <li>
                Commands intended to be used in the .vimrc should be defined in
                a <code>instant/commands.vim</code> file in plugins using
                maktaba, or explicitly installed via an autoload function in
                non-maktaba plugins.
              </li>
            </ul>
          </li>
        </ul>
        <SUBSECTION title="Conventions">
          <ul>
            <li>
              Pass <code>&lt;bang&gt;</code> to functions with
              <code>'&lt;bang&gt;' == '!'</code>.
              <ul>
                <li>
                  The function should receive a boolean parameter, not a string.
                </li>
              </ul>
            </li>
          </ul>
        </SUBSECTION>
      </BODY>
    </STYLEPOINT>

    <STYLEPOINT title="Autocommands">
      <SUMMARY>
        <ul>
          <li>Define in <code>plugin/autocmds.vim</code>.</li>
          <li>Use augroups.</li>
          <li>augroup_names_like_this.</li>
          <li>Clear the augroup first.</li>
          <li>Extract logic into functions.</li>
        </ul>
      </SUMMARY>
      <BODY>
        <ul>
          <li>
            All autocommands should be defined in the
            <code>plugin/autocmds.vim</code> file.
            <ul>
              <li>
                This allows users to disable your autocommands with
                <code>Glaive myplugin !plugin[autocmds]</code>.
              </li>
            </ul>
          </li>
          <li>
            Declare all autocommands in an <code>augroup</code> block.
            <ul>
              <li>
                This allows your autocommands to be cleared with
                <code>autocmd!</code>.
              </li>
              <li>
                If your plugin only has one <code>augroup</code>, the
                <code>augroup</code> name should be the same as your plugin
                name, with underscores in place of any hyphens.
              </li>
              <li>
                Otherwise <code>augroup</code> names should start with your
                plugin name followed by an underscore.
              </li>
            </ul>
          </li>
          <li>
            Do not put logic in autocommands.
            <ul>
              <li>
                Delegate to functions instead.
              </li>
            </ul>
          </li>
          <li>
            When creating a new <code>augroup</code>, clear it with
            <code>autocmd!</code>
            <ul>
              <li>
                This allows your plugins to be re-enterable.
              </li>
            </ul>
          </li>
        </ul>
      </BODY>
    </STYLEPOINT>

    <STYLEPOINT title="Functions">
      <SUMMARY>
        <ul>
          <li>FunctionNamesLikeThis.</li>
          <li>Autoload all functions.</li>
          <li>Prefix script-local functions with <code>s:</code></li>
          <li>Use <code>[!]</code>.</li>
          <li>Use <code>[abort]</code>.</li>
        </ul>
      </SUMMARY>
      <BODY>
        <ul>
          <li>
            <code>FunctionNamesLikeThis</code>
          </li>
          <li>
            Prefix all script-local functions with <code>s:</code>
          </li>
          <li>
            Do not provide global functions. Use autoloaded functions instead.
          </li>
          <li>
            Place two blank lines between top-level functions.
          </li>
          <li>
            Declare all functions with <code>abort</code>.
            <ul>
              <li>
                If you do not do this, the function's behavior depends upon
                whether it is called within a <code>try..endtry</code> block
                somewhere on the stack.
              </li>
              <li>
                The <code>abort</code> keyword forces the function to act
                consistently.
              </li>
              <li>
                Without it, the function may (or may not) attempt to continue
                execution after an error occurs.
              </li>
            </ul>
          </li>
          <li>
            Use <code>function!</code> with a bang.
            <ul>
              <li>
                This allows developers to re-source their scripts and have the
                functions reloaded without complaint.
              </li>
              <li>
                Function names should never collide because functions should
                always be either script-local or defined in an
                <code>autoload</code> directory.
              </li>
              <li>
                Failing to use a bang in any function in an autoload file will
                lead to cryptic errors if vim tries to re-source the file
                (e.g., if you refer to an nonexistent autoload function).
              </li>
            </ul>
          </li>
          <li>
            Use <code>...</code> for optional arguments, not for lists of
            arguments.
            <ul>
              <li>
                Vimscript functions take at most 20 arguments.
              </li>
              <li>
                Lists have no such length restriction.
              </li>
              <li>
                Your function is likely to break when given too many arguments
                if you use <code>...</code> for a list of arguments.
              </li>
            </ul>
          </li>
          <li>
            Throw exceptions rather than printing errors.
            <ul>
              <li>
                Printed errors can not be caught.
              </li>
              <li>
                Top-level functions expecting errors may catch them and print
                error messages, but even those should throw their own errors
                when they choke.
              </li>
            </ul>
          </li>
        </ul>
      </BODY>
    </STYLEPOINT>

    <STYLEPOINT title="Mappings">
      <SUMMARY>
        <ul>
          <li>
            Provide opt-in key mappings in <code>plugin/mappings.vim</code>.
          </li>
          <li>
            <code>&lt;Plug&gt;</code> mappings can be defined in
            <code>plugin/plugs.vim</code> (unlike mappings.vim, plugs.vim is
            opt-out).
          </li>
        </ul>
      </SUMMARY>
      <BODY>
        <ul>
          <li>
            Define key mappings in <code>plugin/mappings.vim</code>, using
            <code>maktaba#plugin#MapPrefix</code> to get a prefix.
            <ul>
              <li>
                Mappings defined in the special <code>plugin/mappings.vim</code>
                file will be disabled by default (by the standard
                <code>maktaba#plugin#Enter()</code> boilerplate).
              </li>
              <li>
                Users can enable key mappings with
                <code>Glaive myplugin plugin[mappings]</code>.
              </li>
            </ul>
          </li>
          <li>
            Make all mappings with <code>&lt;unique&gt;</code>.
            <ul>
              <li>
                This will inform the user when they have a mapping conflict
                instead of silently clobbering their existing mappings.
              </li>
            </ul>
          </li>
          <li>
            You may provide pseudo-mappings using <code>&lt;Plug&gt;</code> and
            your plugin's name in <code>plugin/plugs.vim</code> (separate from
            standard key mappings).
            <ul>
              <li>
                <code>&lt;Plug&gt;</code> is a sequence which can not be typed.
              </li>
              <li>
                You can do something like
                <code>noremap &lt;Plug&gt;namespace#MappingName
                  some_key_sequence</code>
                and then users can do
                <code>noremap &lt;leader&gt;x
                  &lt;Plug&gt;namespace#MappingName</code>
                to take advantage of your pseudo-mapping.
              </li>
              <li>
                Pseudo-mappings should <strong>not</strong> be in
                <code>plugin/mappings.vim</code> or they will be disabled by
                default.
              </li>
              <li>
                Such pseudo-mappings should be named <code>&lt;Plug&gt;</code>
                followed by your plugin name, a pound sign, and a unique mapping
                name (CamelCased like a function).
              </li>
            </ul>
          </li>
          <li>
            Always use the <code>noremap</code> family of commands. Never use
            the <code>map</code> family.
            <ul>
              <li>
                <code>map</code> depends upon the user's existing mappings, and
                could do anything.
              </li>
            </ul>
          </li>
          <li>
            Only use <code>noremap</code> for commands that both make a motion
            and take a range.
            <ul>
              <li>
                <code>noremap</code> makes mappings in normal, visual, and
                operator-pending modes.
              </li>
              <li>
                If you don't want all these use <code>nnoremap</code>
                <code>onoremap</code> or <code>vnoremap</code> explicitly.
              </li>
            </ul>
          </li>
          <li>
            Always use <code>&lt;SID&gt;</code> in place of <code>s:</code> when
            accessing script locals in mappings.
            <ul>
              <li>
                Using <code>s:</code> will often fail as the mapping attempts to
                type a literal s and colon.
              </li>
            </ul>
          </li>
        </ul>
      </BODY>
    </STYLEPOINT>
  </CATEGORY>
  <CATEGORY title="Conventions">
    <STYLEPOINT title="Dependency Checking">
      <SUMMARY>
        Declare dependencies in addon-info.json and use <code>maktaba</code>.
      </SUMMARY>
      <BODY>
        <p>
          Declaring dependencies in addon-info.json allows conformant plugin
          managers (like VAM) to ensure dependencies are installed. See the
          <a href="http://goo.gl/CUXJZC">VAM documentation</a> for details.
        </p>
        <p>
          Calling <code>maktaba#library#Require</code> from dependent code at
          runtime ensures that dependencies have been installed and that they
          don't include unsafe non-library files.
        </p>
      </BODY>
    </STYLEPOINT>

    <STYLEPOINT title="Statusline Flags">
      <SUMMARY>
        Use <code>&lt;plugin-name&gt;#status#Status()</code> or its
        finer-grained variants to provide statusline flags.
      </SUMMARY>
      <BODY>
        <p>
          Following is a convention for exposing statusline flags to the user. A
          plugin should never modify the user's statusline except for when that
          is the only purpose of the plugin (powerline, etc.).
        </p>
        <ul>
          <li>
            Provide the
            <code class="green">Info</code>,
            <code class="yellow">Alert</code>,
            <code class="orange">Warning</code>, and
            <code class="red">Error</code> functions under the
            <code>&lt;plugin-name&gt;#status</code> namespace.
          </li>
          <li>
            <code class="green">Info</code> should provide information about the
            state of the buffer.
            <ul>
              <li>
                Example: The current git branch.
              </li>
            </ul>
          </li>
          <li>
            <code class="yellow">Alert</code> should provide a quiet reminder
            that the buffer is non-standard.
            <ul>
              <li>
                Example: The readonly setting is on.
              </li>
            </ul>
          </li>
          <li>
            <code class="orange">Warning</code> should provide a warning about
            the current state of the buffer.
            <ul>
              <li>
                Example: The file has been edited elsewhere.
              </li>
            </ul>
          </li>
          <li>
            <code class="red">Error</code> should bring to attention a loud
            issue with the buffer.
            <ul>
              <li>
                Example: The file does not pass the syntax checker.
              </li>
            </ul>
          </li>
          <li>
            By following these conventions, users can easily build up their own
            statusline customizing the verbosity and colors to their tastes.
          </li>
          <li>
            All functions should take no arguments and should return either
            empty strings or strings enclosed by square brackets, e.g.
            <code>[Google]</code>. For example:
            <ul>
              <li>
                A trailing whitespace plugin might return <code>[$]</code> if
                the file contains trailing whitespace
              </li>
              <li>
                A prose writing plugin might return <code>[write]</code> if vim
                is in writing mode.
              </li>
            </ul>
          </li>
          <li>
            Consider providing the
            <code>&lt;plugin-name&gt;#status#Status</code> function.
            <ul>
              <li>
                It should return the first non-empty of <code>Error</code>,
                <code>Warning</code>, <code>Alert</code>, or <code>Info</code>.
              </li>
              <li>
                This is useful for users who want only the most relevant flag
                and do not have a colored statusline.
              </li>
            </ul>
          </li>
        </ul>
      </BODY>
    </STYLEPOINT>
  </CATEGORY>
  <CATEGORY title="Forbidden Commands">
    <p>
      These are commands which can only be used by a limited number of
      plugins, and should not in general be used by yours.
    </p>
    <ul>
      <li>
        Do not use <code>:match :2match</code> or <code>:3match</code>
        <ul>
          <li>
            These are reserved for the user and for vim itself.
          </li>
          <li>
            Use <code>matchadd()</code> to create a matchlevel unique to your
            plugin.
          </li>
        </ul>
      </li>
      <li>
        Do not use <code>echoerr</code>.
        <ul>
          <li>
            <code>echoerr</code> does not print the red error message that you
            might think it does.
          </li>
          <li>
            <code>echoerr</code> prints an error message as well as context
            about the code where <code>echoerr</code> was called.
          </li>
          <li>
            <code>echoerr</code> is best suited for debugging.
          </li>
          <li>
            Use <code>echohl</code> in tandem with <code>echomsg</code>  if
            you want the red error bar.
          </li>
        </ul>
      </li>
      <li>
        Use <code>echomsg</code> instead of <code>echo</code>.
        <ul>
          <li>
            <code>echomsg</code> messages can be reviewed with the
            <code>:messages</code> command.
          </li>
          <li>
            <code>echo</code> messages disappear permanently on redraw, which
            can be very annoying to users who failed to read the message in
            time.
          </li>
        </ul>
      </li>
    </ul>
  </CATEGORY>
  <CATEGORY title="Layout">
    <p>
      Lay out <code>plugin/</code> files in the following sections, if
      applicable, separated by two blank lines:
    </p>
    <ul>
      <li>
        Declaration of script constants
      </li>
      <li>
        Declaration of configuration variables
      </li>
      <li>
        Other declarations (commands in <code>commands.vim</code> file,
        autocommands in <code>autocmds.vim</code> file, etc.)
      </li>
    </ul>
    <p>
      Lay out <code>autoload/</code> files in the following sections, if
      applicable, separated by two blank lines:
    </p>
    <ul>
      <li>
        <code>maktaba#library#Require</code> calls
      </li>
      <li>
        Script-local variables
      </li>
      <li>
        Script-local functions
      </li>
      <li>
        Private autoloaded functions
      </li>
      <li>
        Public autoloaded functions
      </li>
    </ul>
    <p>
      This is recommended convention and is not enforced.
    </p>

  </CATEGORY>
  <CATEGORY title="Recommended Shortcuts">
    
    <p>
      Use the following shortcuts:
    </p>
    <ul>
      <li>
        <code>catch</code> over <code>catch /.*/</code>
      </li>
      <li>
        <code>return</code> over <code>return 0</code> when the return value
        has no semantic purpose.
      </li>
    </ul>

  </CATEGORY>
  <CATEGORY title="Errata">
    <p>
      This section plumbs some of the darker corners of vimscript, explaining
      the language pathologies that you wish you didn't have to know.
      
    </p>

    <STYLEPOINT title="Compatibility Mode">
      <SUMMARY>
        If you don't support vi-compatibility mode, fail gracefully.
      </SUMMARY>
      <BODY>
        <p>
          When <code>compatible</code> is set, many vim features are not
          available. The vim feature which most commonly affects vimscript
          authors is line continuations.
        </p>
        <p>
          If you want your plugin to work in vim with vi compatibility on, you
          will need to save the compatibility options at the beginning of each
          plugin file, clear them, and restore them at the end of each plugin
          file. See <code>:help use-cpo-save</code> for details.
        </p>
        <p>
          Plugins that depend on maktaba generally don't need to worry about
          compatible mode since maktaba currently just disables it, printing a
          warning.
        </p>
      </BODY>
    </STYLEPOINT>
  </CATEGORY>

  <p align="right">
    Revision 1.1
  </p>

  
  <address>
    Nate Soares<br/>
    Joshua Hoak<br/>
    David Barnett<br/>
  </address>
</GUIDE>