releaseSelector (elem) {
    if (!elem) { return }
    const N = this.selectors.length
    const sel = this.selectorMap[elem.id]
    if (!sel?.locked) {
      // TODO(codedread): Ensure this exists in this module.
      console.warn('WARNING! selector was released but was already unlocked')
    }
    for (let i = 0; i < N; ++i) {
      if (this.selectors[i] && this.selectors[i] === sel) {
        delete this.selectorMap[elem.id]
        sel.locked = false
        sel.selectedElement = null
        sel.showGrips(false)

        // remove from DOM and store reference in JS but only if it exists in the DOM
        try {
          sel.selectorGroup.setAttribute('display', 'none')
        } catch (e) { /* empty fn */ }

        break
      }
    }
  }
Removes the selector of the given element (hides selection box).

@param {Element} elem - DOM element to remove the selector for
@returns {void}