feat: support columns numbers (and line range) in links fragments

Fixes #7

src/index.js

@@ -11,6 +11,7 @@ const {
   isValidIntegerString,
   getNumberOfLines,
   getLineNumberStringFromFragment,
+  lineFragmentRe,
 } = require("./utils.js")
 
 /** @typedef {import('markdownlint').Rule} MarkdownLintRule */
@@ -133,6 +134,10 @@ const customRule = {
 
             const hasOnlyDigits = isValidIntegerString(lineNumberFragmentString)
             if (!hasOnlyDigits) {
+              if (lineFragmentRe.test(url.hash)) {
+                continue
+              }
+
               onError({
                 lineNumber,
                 detail: `${detail} should have a valid fragment identifier`,

src/utils.js

@@ -4,6 +4,8 @@ const { getHtmlAttributeRe } = require("./markdownlint-rule-helpers/helpers.js")
 
 const markdownIt = new MarkdownIt({ html: true })
 
+const lineFragmentRe = /^#(?:L\d+(?:C\d+)?-L\d+(?:C\d+)?|L\d+)$/
+
 /**
  * Converts a Markdown heading into an HTML fragment according to the rules
  * used by GitHub.
@@ -151,6 +153,7 @@ const getLineNumberStringFromFragment = (fragment) => {
 }
 
 module.exports = {
+  lineFragmentRe,
   convertHeadingToHTMLFragment,
   getMarkdownHeadings,
   getMarkdownIdOrAnchorNameFragments,