[dom] Consider new method: getNodesByType (#37)

Currently it is easy to get element node types from any given element in a document by `getElementsByTagName`, but other node types are less straight forward to access. This has many design implications.

Example 1 - comments
---

Comments exist so that code authors can provide commentary to the code in a way that is immediately available in the source code, but not parsed or processed for user consumption. Although comments are easy for humans to read they are hard to access dynamically, and so are largely worthless for storing any sort of data.

Example 2 - attributes
---

Attributes are easy to access from any given node, but are challenging to access without touch their respective node directly. This is not particularly helpful. It may be more important to know about the status of one or more attributes by name or their values without care for the element on which they reside. For instance if I wanted to find a data attribute dynamically from a large section of a document there would be no simple means to accomplish this.

Example 3 - text nodes
---

The most convenient way to access to text content is to ignore the DOM and instead use the less safe innerHTML property. Even still the innerHTML property does not return merely the text node value, but absolutely everything contained by the element.

All of these issues can be solved by a getNodesByType method.  Such a method should provide the same level of availability as the getElementsByTagName method in that:

* The method is available on all element nodes at node creation
* The method searches all descendants and not just immediate child nodes
* The method returns a node list similar to the limitations expressed by the return value of getElementsByTagName

A functional example written in JavaScript can be found at https://github.com/prettydiff/getNodesByType/blob/master/getNodesByType.js. *The code example automatically applies the proposed method to all element nodes present in the document, but not to element nodes created with the createElement method.*

In order to understand the value of this recommendation I strongly suggest playing with the linked code example on any given large markup document. It is liberating to have this level of immediate access without so much need for walking the DOM tree and without reliance upon a framework.

---
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/dom/issues/37