canFuse (annos, sel) {
    // When more than one annotation overlaps with the current selection
    return (annos.length >= 2 && !sel.isCollapsed())
  }
Checks if annotations could be fused.
    There should be more than one annotation overlaped by current selection.

    @param {Array} annos annotations
    @param {Object} sel selection

    @returns {Boolean} Whether or not annotations could be fused.