Method highlight

packages/quill/src/modules/syntax.ts:117–154

(
    highlight: (text: string, language: string) => Delta,
    forced = false,
  )

  }

  highlight(
    highlight: (text: string, language: string) => Delta,
    forced = false,
  ) {
    if (this.children.head == null) return;
    const nodes = Array.from(this.domNode.childNodes).filter(
      (node) => node !== this.uiNode,
    );
    const text = `${nodes.map((node) => node.textContent).join('\n')}\n`;
    const language = SyntaxCodeBlock.formats(this.children.head.domNode);
    if (forced || this.forceNext || this.cachedText !== text) {
      if (text.trim().length > 0 || this.cachedText == null) {
        const oldDelta = this.children.reduce((delta, child) => {
          // @ts-expect-error
          return delta.concat(blockDelta(child, false));
        }, new Delta());
        const delta = highlight(text, language);
        oldDelta.diff(delta).reduce((index, { retain, attributes }) => {
          // Should be all retains
          if (!retain) return index;
          if (attributes) {
            Object.keys(attributes).forEach((format) => {
              if (
                [SyntaxCodeBlock.blotName, CodeToken.blotName].includes(format)
              ) {
                // @ts-expect-error
                this.formatAt(index, retain, format, attributes[format]);
              }
            });
          }
          // @ts-expect-error
          return index + retain;
        }, 0);
      }
      this.cachedText = text;
      this.forceNext = false;
    }
  }

  html(index: number, length: number) {
    const [codeBlock] = this.children.find(index);