src/language-html/print/children.js/printBetweenLine
function printBetweenLine(prevNode, nextNode) {
  return isTextLikeNode(prevNode) && isTextLikeNode(nextNode)
    ? prevNode.isTrailingSpaceSensitive
      ? prevNode.hasTrailingSpaces
        ? preferHardlineAsLeadingSpaces(nextNode)
          ? hardline
          : line
        : ""
      : preferHardlineAsLeadingSpaces(nextNode)
      ? hardline
      : softline
    : (needsToBorrowNextOpeningTagStartMarker(prevNode) &&
        (hasPrettierIgnore(nextNode) ||
          /**
           *     123<a
           *          ~
           *       ><b>
           */
          nextNode.firstChild ||
          /**
           *     123<!--
           *            ~
           *     -->
           */
          nextNode.isSelfClosing ||
          /**
           *     123<span
           *             ~
           *       attr
           */
          (nextNode.type === "element" && nextNode.attrs.length > 0))) ||
      /**
       *     <img
       *       src="long"
       *                 ~
       *     />123
       */
      (prevNode.type === "element" &&
        prevNode.isSelfClosing &&
        needsToBorrowPrevClosingTagEndMarker(nextNode))
    ? ""
    : !nextNode.isLeadingSpaceSensitive ||
      preferHardlineAsLeadingSpaces(nextNode) ||
      /**
       *       Want to write us a letter? Use our<a
       *         ><b><a>mailing address</a></b></a
       *                                          ~
       *       >.
       */
      (needsToBorrowPrevClosingTagEndMarker(nextNode) &&
        prevNode.lastChild &&
        needsToBorrowParentClosingTagStartMarker(prevNode.lastChild) &&
        prevNode.lastChild.lastChild &&
        needsToBorrowParentClosingTagStartMarker(prevNode.lastChild.lastChild))
    ? hardline
    : nextNode.hasLeadingSpaces
    ? line
    : softline;
}