parseHTML disregards browser generated omitted start tags

[mixonic]

The HTML spec allows for "omitted start tags". These tags are optional when their intended child is the first thing in the parent tag. For example, this is a tbody start tag:

<table>
  <tbody>
    <tr>

The tbody may be omitted, and the browser will accept and render:

<table>
  <tr>

However, the omitted start tag will still be added to the DOM. We now test the string and context to see if the browser is about to perform this cleanup, with a special allowance for disregarding <script tags.

http://www.whatwg.org/specs/web-apps/current-work/multipage/syntax.html#optional-tags describes which tags are omittable. The spec for tbody and colgroup explains this behavior:

http://www.whatwg.org/specs/web-apps/current-work/multipage/tables.html#the-tbody-element
http://www.whatwg.org/specs/web-apps/current-work/multipage/tables.html#the-colgroup-element

With aid from @bantic. tl;dr the spec will show you the way.

[mixonic]

Almost, not quite, one moment.

[mixonic]

Upon further reflection, though this fix is quite workable it is not correctly put in dom helper. The special handling of <script is actually against the spec, and if we need it just for Handlebars templates in Ember then we should not be breaking spec here.

[mixonic]

This is a cleaner version of emberjs/ember.js#5571. In Ember, we ignore <script></script> at the start of a string for Handlebars morphs, which bends the HTML spec suggestions. In HTMLBars we should be stricter.