function _highlight(languageName, codeToHighlight, ignoreIllegals, continuation) {
      const keywordHits = Object.create(null);

      /**
       * Return keyword data if a match is a keyword
       * @param {CompiledMode} mode - current mode
       * @param {string} matchText - the textual match
       * @returns {KeywordData | false}
       */
      function keywordData(mode, matchText) {
        return mode.keywords[matchText];
      }

      function processKeywords() {
        if (!top.keywords) {
          emitter.addText(modeBuffer);
          return;
        }

        let lastIndex = 0;
        top.keywordPatternRe.lastIndex = 0;
        let match = top.keywordPatternRe.exec(modeBuffer);
        let buf = "";

        while (match) {
          buf += modeBuffer.substring(lastIndex, match.index);
          const word = language.case_insensitive ? match[0].toLowerCase() : match[0];
          const data = keywordData(top, word);
          if (data) {
            const [kind, keywordRelevance] = data;
            emitter.addText(buf);
            buf = "";

            keywordHits[word] = (keywordHits[word] || 0) + 1;
            if (keywordHits[word] <= MAX_KEYWORD_HITS) relevance += keywordRelevance;
            if (kind.startsWith("_")) {
              // _ implied for relevance only, do not highlight
              // by applying a class name
              buf += match[0];
            } else {
              const cssClass = language.classNameAliases[kind] || kind;
              emitKeyword(match[0], cssClass);
            }
          } else {
            buf += match[0];
          }
          lastIndex = top.keywordPatternRe.lastIndex;
          match = top.keywordPatternRe.exec(modeBuffer);
        }
        buf += modeBuffer.substring(lastIndex);
        emitter.addText(buf);
      }

      function processSubLanguage() {
        if (modeBuffer === "") return;
        /** @type HighlightResult */
        let result = null;

        if (typeof top.subLanguage === 'string') {
          if (!languages[top.subLanguage]) {
            emitter.addText(modeBuffer);
            return;
          }
          result = _highlight(top.subLanguage, modeBuffer, true, continuations[top.subLanguage]);
          continuations[top.subLanguage] = /** @type {CompiledMode} */ (result._top);
        } else {
          result = highlightAuto(modeBuffer, top.subLanguage.length ? top.subLanguage : null);
        }

        // Counting embedded language score towards the host language may be disabled
        // with zeroing the containing mode relevance. Use case in point is Markdown that
        // allows XML everywhere and makes every XML snippet to have a much larger Markdown
        // score.
        if (top.relevance > 0) {
          relevance += result.relevance;
        }
        emitter.__addSublanguage(result._emitter, result.language);
      }

      function processBuffer() {
        if (top.subLanguage != null) {
          processSubLanguage();
        } else {
          processKeywords();
        }
        modeBuffer = '';
      }

      /**
       * @param {string} text
       * @param {string} scope
       */
      function emitKeyword(keyword, scope) {
        if (keyword === "") return;

        emitter.startScope(scope);
        emitter.addText(keyword);
        emitter.endScope();
      }

      /**
       * @param {CompiledScope} scope
       * @param {RegExpMatchArray} match
       */
      function emitMultiClass(scope, match) {
        let i = 1;
        const max = match.length - 1;
        while (i <= max) {
          if (!scope._emit[i]) { i++; continue; }
          const klass = language.classNameAliases[scope[i]] || scope[i];
          const text = match[i];
          if (klass) {
            emitKeyword(text, klass);
          } else {
            modeBuffer = text;
            processKeywords();
            modeBuffer = "";
          }
          i++;
        }
      }

      /**
       * @param {CompiledMode} mode - new mode to start
       * @param {RegExpMatchArray} match
       */
      function startNewMode(mode, match) {
        if (mode.scope && typeof mode.scope === "string") {
          emitter.openNode(language.classNameAliases[mode.scope] || mode.scope);
        }
        if (mode.beginScope) {
          // beginScope just wraps the begin match itself in a scope
          if (mode.beginScope._wrap) {
            emitKeyword(modeBuffer, language.classNameAliases[mode.beginScope._wrap] || mode.beginScope._wrap);
            modeBuffer = "";
          } else if (mode.beginScope._multi) {
            // at this point modeBuffer should just be the match
            emitMultiClass(mode.beginScope, match);
            modeBuffer = "";
          }
        }

        top = Object.create(mode, { parent: { value: top } });
        return top;
      }

      /**
       * @param {CompiledMode } mode - the mode to potentially end
       * @param {RegExpMatchArray} match - the latest match
       * @param {string} matchPlusRemainder - match plus remainder of content
       * @returns {CompiledMode | void} - the next mode, or if void continue on in current mode
       */
      function endOfMode(mode, match, matchPlusRemainder) {
        let matched = startsWith(mode.endRe, matchPlusRemainder);

        if (matched) {
          if (mode["on:end"]) {
            const resp = new Response(mode);
            mode["on:end"](match, resp);
            if (resp.isMatchIgnored) matched = false;
          }

          if (matched) {
            while (mode.endsParent && mode.parent) {
              mode = mode.parent;
            }
            return mode;
          }
        }
        // even if on:end fires an `ignore` it's still possible
        // that we might trigger the end node because of a parent mode
        if (mode.endsWithParent) {
          return endOfMode(mode.parent, match, matchPlusRemainder);
        }
      }

      /**
       * Handle matching but then ignoring a sequence of text
       *
       * @param {string} lexeme - string containing full match text
       */
      function doIgnore(lexeme) {
        if (top.matcher.regexIndex === 0) {
          // no more regexes to potentially match here, so we move the cursor forward one
          // space
          modeBuffer += lexeme[0];
          return 1;
        } else {
          // no need to move the cursor, we still have additional regexes to try and
          // match at this very spot
          resumeScanAtSamePosition = true;
          return 0;
        }
      }

      /**
       * Handle the start of a new potential mode match
       *
       * @param {EnhancedMatch} match - the current match
       * @returns {number} how far to advance the parse cursor
       */
      function doBeginMatch(match) {
        const lexeme = match[0];
        const newMode = match.rule;

        const resp = new Response(newMode);
        // first internal before callbacks, then the public ones
        const beforeCallbacks = [newMode.__beforeBegin, newMode["on:begin"]];
        for (const cb of beforeCallbacks) {
          if (!cb) continue;
          cb(match, resp);
          if (resp.isMatchIgnored) return doIgnore(lexeme);
        }

        if (newMode.skip) {
          modeBuffer += lexeme;
        } else {
          if (newMode.excludeBegin) {
            modeBuffer += lexeme;
          }
          processBuffer();
          if (!newMode.returnBegin && !newMode.excludeBegin) {
            modeBuffer = lexeme;
          }
        }
        startNewMode(newMode, match);
        return newMode.returnBegin ? 0 : lexeme.length;
      }

      /**
       * Handle the potential end of mode
       *
       * @param {RegExpMatchArray} match - the current match
       */
      function doEndMatch(match) {
        const lexeme = match[0];
        const matchPlusRemainder = codeToHighlight.substring(match.index);

        const endMode = endOfMode(top, match, matchPlusRemainder);
        if (!endMode) { return NO_MATCH; }

        const origin = top;
        if (top.endScope && top.endScope._wrap) {
          processBuffer();
          emitKeyword(lexeme, top.endScope._wrap);
        } else if (top.endScope && top.endScope._multi) {
          processBuffer();
          emitMultiClass(top.endScope, match);
        } else if (origin.skip) {
          modeBuffer += lexeme;
        } else {
          if (!(origin.returnEnd || origin.excludeEnd)) {
            modeBuffer += lexeme;
          }
          processBuffer();
          if (origin.excludeEnd) {
            modeBuffer = lexeme;
          }
        }
        do {
          if (top.scope) {
            emitter.closeNode();
          }
          if (!top.skip && !top.subLanguage) {
            relevance += top.relevance;
          }
          top = top.parent;
        } while (top !== endMode.parent);
        if (endMode.starts) {
          startNewMode(endMode.starts, match);
        }
        return origin.returnEnd ? 0 : lexeme.length;
      }

      function processContinuations() {
        const list = [];
        for (let current = top; current !== language; current = current.parent) {
          if (current.scope) {
            list.unshift(current.scope);
          }
        }
        list.forEach(item => emitter.openNode(item));
      }

      /** @type {{type?: MatchType, index?: number, rule?: Mode}}} */
      let lastMatch = {};

      /**
       *  Process an individual match
       *
       * @param {string} textBeforeMatch - text preceding the match (since the last match)
       * @param {EnhancedMatch} [match] - the match itself
       */
      function processLexeme(textBeforeMatch, match) {
        const lexeme = match && match[0];

        // add non-matched text to the current mode buffer
        modeBuffer += textBeforeMatch;

        if (lexeme == null) {
          processBuffer();
          return 0;
        }

        // we've found a 0 width match and we're stuck, so we need to advance
        // this happens when we have badly behaved rules that have optional matchers to the degree that
        // sometimes they can end up matching nothing at all
        // Ref: https://github.com/highlightjs/highlight.js/issues/2140
        if (lastMatch.type === "begin" && match.type === "end" && lastMatch.index === match.index && lexeme === "") {
          // spit the "skipped" character that our regex choked on back into the output sequence
          modeBuffer += codeToHighlight.slice(match.index, match.index + 1);
          if (!SAFE_MODE) {
            /** @type {AnnotatedError} */
            const err = new Error(`0 width match regex (${languageName})`);
            err.languageName = languageName;
            err.badRule = lastMatch.rule;
            throw err;
          }
          return 1;
        }
        lastMatch = match;

        if (match.type === "begin") {
          return doBeginMatch(match);
        } else if (match.type === "illegal" && !ignoreIllegals) {
          // illegal match, we do not continue processing
          /** @type {AnnotatedError} */
          const err = new Error('Illegal lexeme "' + lexeme + '" for mode "' + (top.scope || '<unnamed>') + '"');
          err.mode = top;
          throw err;
        } else if (match.type === "end") {
          const processed = doEndMatch(match);
          if (processed !== NO_MATCH) {
            return processed;
          }
        }

        // edge case for when illegal matches $ (end of line) which is technically
        // a 0 width match but not a begin/end match so it's not caught by the
        // first handler (when ignoreIllegals is true)
        if (match.type === "illegal" && lexeme === "") {
          // advance so we aren't stuck in an infinite loop
          return 1;
        }

        // infinite loops are BAD, this is a last ditch catch all. if we have a
        // decent number of iterations yet our index (cursor position in our
        // parsing) still 3x behind our index then something is very wrong
        // so we bail
        if (iterations > 100000 && iterations > match.index * 3) {
          const err = new Error('potential infinite loop, way more iterations than matches');
          throw err;
        }

        /*
        Why might be find ourselves here?  An potential end match that was
        triggered but could not be completed.  IE, `doEndMatch` returned NO_MATCH.
        (this could be because a callback requests the match be ignored, etc)

        This causes no real harm other than stopping a few times too many.
        */

        modeBuffer += lexeme;
        return lexeme.length;
      }

      const language = getLanguage(languageName);
      if (!language) {
        error(LANGUAGE_NOT_FOUND.replace("{}", languageName));
        throw new Error('Unknown language: "' + languageName + '"');
      }

      const md = compileLanguage(language);
      let result = '';
      /** @type {CompiledMode} */
      let top = continuation || md;
      /** @type Record<string,CompiledMode> */
      const continuations = {}; // keep continuations for sub-languages
      const emitter = new options.__emitter(options);
      processContinuations();
      let modeBuffer = '';
      let relevance = 0;
      let index = 0;
      let iterations = 0;
      let resumeScanAtSamePosition = false;

      try {
        if (!language.__emitTokens) {
          top.matcher.considerAll();

          for (; ;) {
            iterations++;
            if (resumeScanAtSamePosition) {
              // only regexes not matched previously will now be
              // considered for a potential match
              resumeScanAtSamePosition = false;
            } else {
              top.matcher.considerAll();
            }
            top.matcher.lastIndex = index;

            const match = top.matcher.exec(codeToHighlight);
            // console.log("match", match[0], match.rule && match.rule.begin)

            if (!match) break;

            const beforeMatch = codeToHighlight.substring(index, match.index);
            const processedCount = processLexeme(beforeMatch, match);
            index = match.index + processedCount;
          }
          processLexeme(codeToHighlight.substring(index));
        } else {
          language.__emitTokens(codeToHighlight, emitter);
        }

        emitter.finalize();
        result = emitter.toHTML();

        return {
          language: languageName,
          value: result,
          relevance,
          illegal: false,
          _emitter: emitter,
          _top: top
        };
      } catch (err) {
        if (err.message && err.message.includes('Illegal')) {
          return {
            language: languageName,
            value: escape(codeToHighlight),
            illegal: true,
            relevance: 0,
            _illegalBy: {
              message: err.message,
              index,
              context: codeToHighlight.slice(index - 100, index + 100),
              mode: err.mode,
              resultSoFar: result
            },
            _emitter: emitter
          };
        } else if (SAFE_MODE) {
          return {
            language: languageName,
            value: escape(codeToHighlight),
            illegal: false,
            relevance: 0,
            errorRaised: err,
            _emitter: emitter,
            _top: top
          };
        } else {
          throw err;
        }
      }
    }
private highlight that's used internally and does not fire callbacks

@param {string} languageName - the language to use for highlighting
@param {string} codeToHighlight - the code to highlight
@param {boolean?} [ignoreIllegals] - whether to ignore illegal matches, default is to bail
@param {CompiledMode?} [continuation] - current continuation mode, if any
@returns {HighlightResult} - result of the highlight operation