This allows selecting particular attributes by name but without specifying the value and similar to xpath syntax `[@attrib]`
Now dots are parsed. For example '87 Min.'
In a strict sense such TTML is invalid, but Yahoo uses it.
This function is used only in SohuIE, which is updated to use a new extraction logic.
Fixes #2865, closes #5087
Previously, the runtime could be atrocious for longer inputs.
This functionality is intended to eventually encompass the current format filtering.
Reported at https://news.ycombinator.com/item?id=8648121