2.2.1 [W3C-TTML-1.0] Section 7.2.3, xml:space

C0002:

The specification states:

 The xml:space attribute is used as defined by 
 [XML 1.0], §2.10, White Space Handling.
 The xml:space attribute may be used with any element in the core vocabulary catalog.

IE10 Mode, IE11 Mode, and EdgeHTML Mode (All Versions)

The xml:space attribute is ignored. Whitespace is ignored.