"Styling with XML" Heading definition not taking effect

[gy9527]

I need to define styles using XML. So, I tested this example code (demo/13-xml-styles.ts), but the example didn't execute as expected: line 15 of the code didn't take effect, it only generated the body format.

For this sample code, if I don't use "externalStyles," line 15 of the code works; however, after introducing XML-defined styles, the "heading" definition becomes ineffective.