Google Apps Script: How to determine if a range within a Google Doc contains a given position.

Code.gs

/**
 * Determines if a range within a Google Doc contains a given position.
 * @param {DocumentApp.Range} range A range within the document.
 * @param {DocumentApp.Position} psoition A position within the document.
 * @return {boolean} True if the position falls within the range, false otherwise.
 */
function rangeContainsPosition(range, position) {
  var positionElement = position.getElement();
  var positionOffest = position.getOffset();
  
  // If the the position is a container element, get the actual element it points to.
  if (positionElement.getNumChildren && positionElement.getNumChildren() > 0) {
    // If the position is at the end of a container, get the last element.
    if (positionElement.getNumChildren() <= positionOffest) {
      positionOffest = positionElement.getNumChildren() - 1;
    }
    positionElement = positionElement.getChild(positionOffest);
    positionOffest = 0;
  }
  var positionElementPath = getElementPath(positionElement);
  
  // Look through all the elements in the range.
  var rangeElements = range.getRangeElements();
  for (var i = 0; i < rangeElements.length; i++) {
    var rangeElement = rangeElements[i];
    var rangeElementPath = getElementPath(rangeElement.getElement());
    
    // Are they the same element?
    if (rangeElementPath == positionElementPath) {
      if (rangeElement.isPartial()) {
        return positionOffest >= rangeElement.getStartOffset() && 
               positionOffest <= rangeElement.getEndOffsetInclusive();
      } else {
        return true;
      }
    // Is position element contained within range element?
    } else if (positionElementPath.indexOf(rangeElementPath) == 0) {
      return true;
    }
  }
  return false;
}

/**
 * Gets the path of an element within the document.
 * @param {DocumentApp.Element} element The element to evaluate.
 * @return {string} The path of an element within the document.
 */
function getElementPath(element) {
  var parts = [];
  while (element.getParent()) {
    var parent = element.getParent();
    var pathSegment = Utilities.formatString('%s[%d]', element.getType(), parent.getChildIndex(element));
    parts.unshift(pathSegment);
    element = parent;
  }
  return parts.join('.');
}