Function onMouseDown

static/editor.md/lib/codemirror/lib/codemirror.js:3445–3480

(e)

  // middle-click-paste. Or it might be a click on something we should
  // not interfere with, such as a scrollbar or widget.
  function onMouseDown(e) {
    var cm = this, display = cm.display;
    if (display.activeTouch && display.input.supportsTouch() || signalDOMEvent(cm, e)) return;
    display.shift = e.shiftKey;

    if (eventInWidget(display, e)) {
      if (!webkit) {
        // Briefly turn off draggability, to allow widgets to do
        // normal dragging things.
        display.scroller.draggable = false;
        setTimeout(function(){display.scroller.draggable = true;}, 100);
      }
      return;
    }
    if (clickInGutter(cm, e)) return;
    var start = posFromMouse(cm, e);
    window.focus();

    switch (e_button(e)) {
    case 1:
      if (start)
        leftButtonDown(cm, e, start);
      else if (e_target(e) == display.scroller)
        e_preventDefault(e);
      break;
    case 2:
      if (webkit) cm.state.lastMiddleDown = +new Date;
      if (start) extendSelection(cm.doc, start);
      setTimeout(function() {display.input.focus();}, 20);
      e_preventDefault(e);
      break;
    case 3:
      if (captureRightClick) onContextMenu(cm, e);
      break;
    }
  }

  var lastClick, lastDoubleClick;
  function leftButtonDown(cm, e, start) {