Implements ConvertCREToStandard which converts CREngine XPointers
(e.g. /body/DocFragment[6]/body/div/p[47]/text().2399) to standard
epubcfi format (e.g. epubcfi(/6/12!/4/2[id]/4/1:7)).
Key components:
- indexChildNodes: faithful port of foliate-js's epubcfi.js algorithm
for computing CFI-compatible child node indices including virtual
positions, null positions between adjacent elements, and text chunks
- preprocessXHTML: converts XHTML self-closing tags (e.g. <a id="x"/>)
to open/close pairs so Go's HTML parser produces the same DOM as the
browser's XHTML parser
- buildCFI: walks up from a text node to body, computing CFI indices
at each level using indexChildNodes
- findTextInNode: regex-based whitespace-flexible text search for
context_text fallback positioning
- convertByPercentageOffset: estimates position via book-wide character
counts when no context_text is available
- ConvertCREToStandard: orchestrates text search → percentage fallback
Supports CREngine XPointer format, CREngine fragment ID format
(#_doc_fragment_N_anchor), and includes round-trip test coverage for
1984 and Crime and Punishment EPUBs.
