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