Function Selection

static/editor.md/lib/codemirror/lib/codemirror.js:1917–1920

(ranges, primIndex)

  // which one is the primary selection (the one that's scrolled into
  // view, that getCursor returns, etc).
  function Selection(ranges, primIndex) {
    this.ranges = ranges;
    this.primIndex = primIndex;
  }

  Selection.prototype = {
    primary: function() { return this.ranges[this.primIndex]; },