2.1.1553 Part 1 Section 21.2.2.210, title (Title)

a.   The standard describes the tx child element as optional but does not state default value.

In Office, the default text in the title is a localized string specific to the parent element type, except when this element is the child of a chart that has a single series with a name, in which case the text shall be that series' name.

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