Function hasBadBidiRects

static/editor.md/lib/codemirror/lib/codemirror.js:8275–8282

(measure)

  // Feature-detect IE's crummy client rect reporting for bidi text
  var badBidiRects;
  function hasBadBidiRects(measure) {
    if (badBidiRects != null) return badBidiRects;
    var txt = removeChildrenAndAdd(measure, document.createTextNode("A\u062eA"));
    var r0 = range(txt, 0, 1).getBoundingClientRect();
    if (!r0 || r0.left == r0.right) return false; // Safari returns null in some cases (#2780)
    var r1 = range(txt, 1, 2).getBoundingClientRect();
    return badBidiRects = (r1.right - r0.right < 3);
  }

  // See if "".split is the broken IE version, if so, provide an
  // alternative way to split lines.