TagBuilder can't build valueless attributes

[geertdoornbos]

The Tagbuilder can't build a tag that had attributes with no value, like:

<script src="..." async></script>

It is currently possible to build alternatives:
<script src="..." async=""></script>
or
<script src="..." async="async"></script>

All three ways should be possible, where the first is the most clean way.

[dougbu]

Suspect you'd be better served using TagHelperOutput. On one hand TagBuilder is intended for HTML generation from code and we long-ago chose to emit only XHTML syntax. On the other, TagHelperOutput is intended to maintain the original syntax (from a .cshtml file) when filtering that HTML through a tag helper.

In any case TagBuilder does not support minimized attributes, sorts the generated attributes alphabetically by name, and more.