[RavSinghChandan]

set_page_label validates its indices, its start and that a style or prefix is given, but not the style itself:

>>> writer.set_page_label(0, 2, "/Nonsense")
>>> PdfReader(out).page_labels
['1', '2', '3']  # the style was dropped

index2label logs "Ignoring unknown page label numbering style" and falls back to the page position, so the caller is left with plain numbers and a log line.

The style was also annotated Optional[PageLabelStyle], which is a plain class holding the five string constants rather than a type any caller can satisfy - every caller passes "/D". Typed as the literal strings it takes, which clears two typeguard failures.

Reverting the change fails the four new tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.00%. Comparing base (0b0721e) to head (dc5edf8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4017   +/-   ##
=======================================
  Coverage   98.00%   98.00%           
=======================================
  Files          57       57           
  Lines       11143    11145    +2     
  Branches     2091     2092    +1     
=======================================
+ Hits        10921    10923    +2     
  Misses        124      124           
  Partials       98       98           

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[RavSinghChandan]

Agreed, that's the better fix. PageLabelStyle is a StrEnum now like FilterTypes, so the annotation can name it directly and the separate alias is gone.