Function moveOnce

static/editor.md/lib/codemirror/lib/codemirror.js:4646–4655

(boundToLine)

      return lineObj = getLine(doc, l);
    }
    function moveOnce(boundToLine) {
      var next = (visually ? moveVisually : moveLogically)(lineObj, ch, dir, true);
      if (next == null) {
        if (!boundToLine && findNextLine()) {
          if (visually) ch = (dir < 0 ? lineRight : lineLeft)(lineObj);
          else ch = dir < 0 ? lineObj.text.length : 0;
        } else return (possible = false);
      } else ch = next;
      return true;
    }

    if (unit == "char") moveOnce();
    else if (unit == "column") moveOnce(true);