showSourceEditor (e, forSaving) {
    const $editorDialog = document.getElementById('se-svg-editor-dialog')
    if ($editorDialog.getAttribute('dialog') === 'open') return
    const origSource = this.editor.svgCanvas.getSvgString()
    $editorDialog.setAttribute('dialog', 'open')
    $editorDialog.setAttribute('value', origSource)
    $editorDialog.setAttribute('copysec', Boolean(forSaving))
    $editorDialog.setAttribute('applysec', !forSaving)
  }
@param {Event} [e] Not used.
@param {boolean} forSaving
@returns {void}