Constrained Highlight/Mark Broken

[tajmone]

• [x] Add tests for constrained mark element.
• [x] Try and understand better the problem. (it just works now, maybe the problem was elsewhere)
• [x] Fix the syntax.

---

The constrained mark element (mark) had to be temporarily disabled because it was causing major documents disruptions (this element was possibly the main problem in the original syntax).

The problem affects the constrained variant only; the unconstrained mark element (mark_double) is still enabled, tested for, and working fine.

  ##################
  # MARK CONSTRAINED
  ##################
  # Was: "MARK"
  # Marked text (constrained variant).
  # Examples:
  #   #Lorem ipsum# dolor
  #   [red]#Lorem ipsum# dolor

From my annotated comments, it seems that the problem is in the optional "start with attribute" definition, which matches wildly.

References

• AsciiDoc Language Documentation:
  • Text Formatting and Punctuation:
    • Highlight
    • Constrained formatting pair
    • Unconstrained formatting pair
    • Troubleshoot Unconstrained Formatting Pairs