Update README.md to clarify two things.

README.md

@@ -70,6 +70,13 @@ and test cases came directly from that project.
 [super-linter]: https://github.com/github/super-linter
 [vscode-markdownlint]: https://marketplace.visualstudio.com/items?itemName=DavidAnson.vscode-markdownlint
 
+### References
+
+The following specifications are considered authoritative in cases of ambiguity:
+
+- [CommonMark](https://spec.commonmark.org/current/)
+- [GitHub Flavored Markdown Spec](https://github.github.com/gfm/)
+
 ## Demonstration
 
 [`markdownlint` demo](https://dlaa.me/markdownlint/), an interactive, in-browser
@@ -185,7 +192,7 @@ rules at once.
 ## Configuration
 
 Text passed to `markdownlint` is parsed as Markdown, analyzed, and any
-issues reported. Two kinds of text are ignored:
+issues reported. Two kinds of text are ignored by most rules:
 
 - [HTML comments](https://www.w3.org/TR/html5/syntax.html#comments)
 - [Front matter](https://jekyllrb.com/docs/frontmatter/) (see

test/markdownlint-test.js

@@ -639,6 +639,7 @@ test("readmeHeadings", (t) => new Promise((resolve) => {
           "## Install",
           "## Overview",
           "### Related",
+          "### References",
           "## Demonstration",
           "## Rules / Aliases",
           "### Custom Rules",
@@ -860,6 +861,7 @@ test("readme", (t) => new Promise((resolve) => {
       t.falsy(err);
       const rulesLeft = [ ...rules ];
       let seenRelated = false;
+      let seenReferences = false;
       let seenRules = false;
       let inRules = false;
       let seenTags = false;
@@ -872,6 +874,8 @@ test("readme", (t) => new Promise((resolve) => {
         ) {
           if (!seenRelated) {
             seenRelated = true;
+          } else if (!seenReferences) {
+            seenReferences = true;
           } else if (!seenRules) {
             seenRules = true;
             inRules = true;