src/language-html/print-preprocess.js/isTarget
function mergeIeConditonalStartEndCommentIntoElementOpeningTag(
  ast /*, options */
) {
  /**
   *     <!--[if ...]><!--><target><!--<![endif]-->
   */
  const isTarget = (node) =>
    node.type === "element" &&
    node.prev &&
    node.prev.type === "ieConditionalStartComment" &&
    node.prev.sourceSpan.end.offset === node.startSourceSpan.start.offset &&
    node.firstChild &&
    node.firstChild.type === "ieConditionalEndComment" &&
    node.firstChild.sourceSpan.start.offset === node.startSourceSpan.end.offset;
  return ast.map((node) => {
    if (node.children) {
      const isTargetResults = node.children.map(isTarget);
      if (isTargetResults.some(Boolean)) {
        const newChildren = [];

        for (let i = 0; i < node.children.length; i++) {
          const child = node.children[i];

          if (isTargetResults[i + 1]) {
            // ieConditionalStartComment
            continue;
          }

          if (isTargetResults[i]) {
            const ieConditionalStartComment = child.prev;
            const ieConditionalEndComment = child.firstChild;

            const startSourceSpan = new ParseSourceSpan(
              ieConditionalStartComment.sourceSpan.start,
              ieConditionalEndComment.sourceSpan.end
            );
            const sourceSpan = new ParseSourceSpan(
              startSourceSpan.start,
              child.sourceSpan.end
            );

            newChildren.push(
              child.clone({
                condition: ieConditionalStartComment.condition,
                sourceSpan,
                startSourceSpan,
                children: child.children.slice(1),
              })
            );

            continue;
          }

          newChildren.push(child);
        }

        return node.clone({ children: newChildren });
      }
    }
    return node;
  });
}