From a3a66ecab2cb8bf9dc43441c7536c38dd75eb65b Mon Sep 17 00:00:00 2001
From: Taylor Hodge <j.taylor.hodge@gmail.com>
Date: Thu, 5 Sep 2024 11:11:05 -0700
Subject: [PATCH] feat: add regex character classes til

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+# Character Classes Are a Sub-language of Regex
+
+Regular expression character classes are their own micro-universe within the regex syntax.
+
+The usual rules for regex we normally find outside of character classes don't apply.
+
+Rules inside character classes are different from the rest of the regex, and treating them the same can lead to errors. For instance:
+
+- The dot `.` loses its "match any character" meaning inside a character class.
+- The caret `^` means "not" at the start of a character class, but matches a literal caret elsewhere.
+- The hyphen `-` defines a range between two characters, but only if it's not at the start or end of the class.
+
+Understanding these differences can help avoid common regex mistakes and write more accurate patterns.
+
+## Basic Character Class
+
+A character class is defined by square brackets `[ ]`. It matches any single character from the set of characters inside the brackets. E.g.
+
+This pattern...
+
+```regex
+[aeiou]
+```
+
+...matches any single vowel.
+
+## Negated Character Class
+
+Adding a caret `^` at the start of a character class negates it, meaning it matches any character that is not in the set. E.g.
+
+This pattern...
+
+```regex
+[^0-9]
+```
+
+...matches any single character that is not a digit.
+
+## Ranges
+
+Inside a character class, you can define ranges using a hyphen `-`. E.g.
+
+This pattern...
+
+```regex
+[a-z]
+```
+
+...matches any single lowercase letter, from a to z.
+
+## Special Characters
+
+Many special characters that have meaning outside of character classes lose their special meaning inside them.
+E.g.
+
+This pattern...
+
+```regex
+[.]
+```
+
+...matches a literal period — _NOT_ the "match any character" that `.` means outside of character classes.
+
+## Meta-characters within Character Classes
+
+Some meta-characters retain special meaning even within character classes:
+
+- `^`: negation (if it's the first character in the class)
+- `-`: range (if it's not the first or last character in the class)
+- `\`: literal
+
+E.g. this pattern...
+
+```regex
+[^-]
+```
+
+...matches any single character that is not a hyphen.
+
+## Predefined Character Classes
+
+Some shorthand character classes exist, which are equivalent to longer character class expressions:
+
+- `\d` is equivalent to `[0-9]`
+- `\w` is equivalent to `[a-zA-Z0-9_]`
+- `\s` is equivalent to `[ \t\r\n\f]`