Function zeroWidthElement

static/editor.md/lib/codemirror/lib/codemirror.js:8260–8271

(measure)

  var zwspSupported;
  function zeroWidthElement(measure) {
    if (zwspSupported == null) {
      var test = elt("span", "\u200b");
      removeChildrenAndAdd(measure, elt("span", [test, document.createTextNode("x")]));
      if (measure.firstChild.offsetHeight != 0)
        zwspSupported = test.offsetWidth <= 1 && test.offsetHeight > 2 && !(ie && ie_version < 8);
    }
    var node = zwspSupported ? elt("span", "\u200b") :
      elt("span", "\u00a0", null, "display: inline-block; width: 1px; margin-right: -1px");
    node.setAttribute("cm-text", "");
    return node;
  }

  // Feature-detect IE's crummy client rect reporting for bidi text
  var badBidiRects;