Spec draft for fromLiteral method. See #347.

spec/index.bs

@@ -24,13 +24,16 @@ Boilerplate: idl-index no
 <pre class="anchors">
 spec: DOM-Parsing; urlPrefix: https://w3c.github.io/DOM-Parsing/
     type: enum; text: SupportedType
+    type: abstract-op; text: fragment parsing algorithm; url: html-fragment-parsing-algorithm
 spec: DOM-Parsing; url: https://w3c.github.io/DOM-Parsing/#dom-innerhtml; type: interface; text: InnerHTML
 urlPrefix: https://html.spec.whatwg.org/multipage/common-dom-interfaces.html; type: dfn; spec: HTML
     text: reflect
 url: https://heycam.github.io/webidl/#this; type: dfn; spec: WebIDL
     text: this
 spec:ECMA-262; urlPrefix: https://tc39.github.io/ecma262/
     type:abstract-op; text:ToString; url: sec-tostring
+    type:abstract-op; text:Get; url: sec-get-o-p
+    type:dfn; text:current realm record; url: current-realm
 </pre>
 
 <pre class="link-defaults">
@@ -285,6 +288,7 @@ wrappers around a string, constructed via a {{TrustedTypePolicy}}'s
 interface TrustedHTML {
   stringifier;
   DOMString toJSON();
+  static TrustedHTML fromLiteral(object templateStringsArray);
 };
 </pre>
 
@@ -297,6 +301,9 @@ will never change during its lifetime.
 TrustedHTML object are to return the value from its
 `[[Data]]` internal slot.
 
+The <dfn method for="TrustedHTML">fromLiteral(object templateStringsArray)</dfn> method, when invoked, returns the result of executing a [$Create a Trusted Type from literal$] algorithm,
+with {{TrustedHTML}} as |type| and |templateStringsArray| as |template|.
+
 ### <dfn interface>TrustedScript</dfn> ### {#trusted-script}
 
 The TrustedScript interface represents a string with an uncompiled
@@ -311,6 +318,7 @@ around a string, constructed via a {{TrustedTypePolicy}}'s
 interface TrustedScript {
   stringifier;
   DOMString toJSON();
+  static TrustedScript fromLiteral(object templateStringsArray);
 };
 </pre>
 
@@ -323,6 +331,8 @@ will never change during its lifetime.
 TrustedScript object are to return the value from its
 `[[Data]]` internal slot.
 
+The <dfn method for="TrustedScript">fromLiteral(object templateStringsArray)</dfn> method, when invoked, returns the result of executing a [$Create a Trusted Type from literal$] algorithm,
+with {{TrustedScript}} as |type| and |templateStringsArray| as |template|.
 
 ### <dfn interface>TrustedScriptURL</dfn> ### {#trused-script-url}
 
@@ -338,6 +348,7 @@ string, constructed via a {{TrustedTypePolicy}}'s
 interface TrustedScriptURL {
   stringifier;
   USVString toJSON();
+  static TrustedScriptURL fromLiteral(object templateStringsArray);
 };
 </pre>
 
@@ -350,6 +361,8 @@ will never change during its lifetime.
 TrustedScriptURL object are to return the value from its
 `[[Data]]` internal slot.
 
+The <dfn method for="TrustedScriptURL">fromLiteral(object templateStringsArray)</dfn> method, when invoked, returns the result of executing a [$Create a Trusted Type from literal$] algorithm,
+with {{TrustedScriptURL}} as |type| and |templateStringsArray| as |template|.
 
 ## <dfn>Policies</dfn> ## {#policies-hdr}
 
@@ -916,6 +929,30 @@ a string |value| and a list |arguments|, execute the following steps:
     Note: This adds an integration point with [dynamic-code-brand-checks proposal](https://tc39.es/proposal-dynamic-code-brand-checks/).
 1.  Return |trustedObject|.
 
+## <dfn abstract-op>Create a Trusted Type from literal</dfn> ## {#create-a-trusted-type-from-literal-algorithm}
+
+Given a {{TrustedType}} type |type| and an object |template|, execute the following steps:
+
+1.  If [$check templatedness$] of |template| returns false, throw a {{TypeError}}.
+1.  If [$Get$](|template|, "length") is not equal to 1, throw a {{TypeError}}.
+1.  Let |templatedValue| be the result of [$Get$](|template|, 1), stringified.
+1.  If |type| is {{TrustedHTML}}, perform the following steps:
+    1.  Let |templateNode| be the results of [=create an element|creating an element=] with "template" as a <var ignore>localName</var>, [=HTML namespace=] as <var ignore>namespace</var>, and current document as <var ignore>document</var>.
+    1.  Assert: |templateNode| is {{HTMLTemplateElement}}.
+    1.  Let |fragment| be the result of invoking [$fragment parsing algorithm$], with |templatedValue| as <var ignore>markup</var>, and |templateNode| as a <var ignore>context element</var>.
+    1.  Set |templatedValue| to be the result of invoking [=HTML fragment serialization algorithm=], with |fragment| as <var ignore>the node</var>.
+
+1. Return a new instace of an interface |type|, with its `[[Data]]` internal slot value set to |templatedValue|.
+
+## Check templatedness of an object ## {#check-templatedness-algorithm}
+
+To <dfn abstract-op>check templatedness</dfn> of an object |value|, perform the following steps. They return a boolean value:
+
+1. If |value| is not a Array exotic object, return false.
+1. Let |realm| be the <a>current Realm Record</a>.
+1. For each |item| of |realm|'s `[[TemplateMap]]` field, if |item|'s `[[Array]]` slot is |value|, return true.
+1. Return false.
+
 ## <dfn abstract-op>Get Trusted Type compliant string</dfn> ## {#get-trusted-type-compliant-string-algorithm}
 
 This algorithm will return a string that can be used with an