2.1.101 Part 1 Section 17.3.2.44, webHidden (Web Hidden Text)

a.   The standard states that this setting shall cause content to be hidden from display at display time in a document when the document is being displayed in a web page view.

Word ignores this setting when it is applied as part of a character style definition.

b.   The standard states that this element specifies whether the contents of this run shall be hidden from display at display time in a document when the document is being displayed in a web page view.

If this element is present within the previous run properties for a run, Word will apply that setting to the current run properties when it is saved.