2.1.1561 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.

b.   The standard describes the tx child element but does not state a requirement for a default character property.

In Office, the title element requires default character properties or direct formatting character properties. See rPr ("[ISO/IEC-29500-1] §21.1.2.3.9; rPr") and defRPr ("[ISO/IEC-29500-1] §21.1.2.3.2; defRPr") elements.