Add specific constructions to test book for testing

[martinpub]

Target test book: X50525A (to be uploaded)

Ensure that the following items are in place:

• [x] Frontmatter, bodymatter, and backmatter sections
• [x] Cover with jacket flaps
• [x] Title page with title and subtitle
• [x] Pagebreaks, inline and block (all page types)
• [x] Part sudvision
• [x] Bridgehead headings
• [x] Figure with figcaption
• [x] Figure with extracted text
• [x] Image series
• [x] Alt texts
• [x] Numbered lists
• [x] Unnumbered lists
• [x] Content document ToC
• [x] Table
• [x] Definition list
• [x] Footnotes
• [x] Endnotes
• [x] Aside text box
• [x] Div text box
• [x] Computer code
• [x] Verse including indent classes and author line
• [x] Blockquotes
• [x] hr thematic breaks
• [x] MathML and ASCIIMath-only math
• [x] Placeholders for User Input Areas

[martinpub]

Hi @AndersEkl, I was checking the endnotes and it seems they are preformatted. Should we update them to be properly numbered by HTML instead of using @class="plain"?

[martinpub]

Most of these additions are in PR #468. Some validation issues.