Refine enum naming doc: compound acronyms, type names are separate

Two clarifications surfaced while applying the rule to the new
imgcodecs enums:

- The "standalone acronym" exception only applies when nothing else
  is glued onto the acronym. Once it's a compound (TiffResUnit,
  CcittRle), PascalCase the whole thing -- an ALL-CAPS-then-lowercase
  transition mid-identifier is harder to read than a clean compound.
  This is also why Lzw/Jbig/Dcs/Rle stayed PascalCase even standalone:
  local consistency within one enum beats selectively all-capping
  only some acronym-derived values.
- Enum *type* names are out of scope for this rule entirely -- they
  mirror the C++ type identifier verbatim (including OpenCV's own
  inconsistent Tiff-vs-JPEG/EXR/PNG/PAM casing), which is how this
  codebase already named ImwriteEXRTypeFlags/ImwritePNGFlags/
  ImwritePAMFlags before this rule existed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: shimat

.github/copilot-instructions.md

@@ -170,12 +170,16 @@ See `src/OpenCvSharpExtern/ximgproc_EdgeDrawing.h`, `src/OpenCvSharp/Modules/xim
 
 C++ enum members are `ALL_CAPS_WITH_UNDERSCORES` (e.g. `IMWRITE_JPEG_QUALITY`, `NORM_L2SQR`). When wrapping them as a C# enum, **default to PascalCase**, stripping the module/family prefix (`IMWRITE_JPEG_QUALITY` → `JpegQuality`). Keep the original casing (or a near-verbatim form) only when one of these narrow exceptions applies:
 
-1. **The value itself is an unbreakable acronym/abbreviation.** Test: read it aloud — do you spell out the letters (like an acronym) rather than pronounce it as a word? If so, PascalCasing it (`Exif`, `L2Sqr`) destroys the acronym for no benefit. Keep it verbatim (`EXIF`, `L2SQR`). Precedent: `NormTypes.INF`/`L1`/`L2SQR`, `ImageMetadataType.EXIF`/`XMP`/`ICCP`/`CICP`.
+1. **The value itself is an unbreakable acronym/abbreviation, standing alone (nothing else glued onto it).** Test: read it aloud — do you spell out the letters (like an acronym) rather than pronounce it as a word? If so, PascalCasing it (`Exif`, `L2Sqr`) destroys the acronym for no benefit. Keep it verbatim (`EXIF`, `L2SQR`). Precedent: `NormTypes.INF`/`L1`/`L2SQR`, `ImageMetadataType.EXIF`/`XMP`/`ICCP`/`CICP`.
 2. **The value has no natural word boundaries — it's an opaque code, not a phrase.** Test: does inserting word breaks add any information, or does it just capitalize letters arbitrarily? If the latter, keep it verbatim. Precedent: `ColorConversionCodes.BGR2GRAY` (whole body kept verbatim, only the `COLOR_` prefix stripped), `FASTType.TYPE_5_8`.
 3. **The prefix identifies a specific vendor/backend and is semantically load-bearing.** Test: does stripping the prefix delete information a reader needs (which camera SDK/backend this property belongs to)? If so, keep the prefix verbatim; the suffix can still be PascalCased normally. Precedent: `VideoCaptureProperties`' `XI_`/`OPENNI_`/`PVAPI_`/`GIGA_`/`IOS_`-prefixed members.
 
 When none of the three applies, PascalCase — don't keep a verbatim name "to be safe." The exceptions are narrow and should be justifiable by one of the tests above, not a default.
 
+**Compounds win over exception 1.** The "standalone" qualifier in exception 1 matters: once an acronym is glued to another word/acronym to form one compound member name, PascalCase the whole compound rather than leaving the acronym in caps — an ALL-CAPS-then-lowercase transition mid-identifier (`TIFFResUnit`, `CCITTRle`) is harder to read than a clean compound (`TiffResUnit`, `CcittRle`). This is why the pre-existing `ImwriteFlags.TiffResUnit`/`JpegQuality`/`PngCompression`/`PamTupleType` PascalCase acronyms that would otherwise qualify for exception 1 in isolation — they're prefixes in a compound, not standalone values. Same reasoning covers `ImwriteTiffCompressionFlags.CcittRle`/`CcittFax3` and the standalone-but-left-PascalCase `Lzw`/`Jbig`/`Dcs`/`Rle` siblings in that same enum (and its `ImwriteEXRCompressionFlags`/`ImwriteHDRCompressionFlags` cousins) — treating every acronym-derived compression-scheme name as ordinary vocabulary, consistently within the enum, beats selectively all-capping only some of them.
+
+**Enum type names are a separate question — mirror the C++ type identifier verbatim, don't run it through this heuristic.** OpenCV's own C++ type names are inconsistently cased across acronyms (`ImwriteJPEGSamplingFactorParams`, `ImwriteEXRTypeFlags`, `ImwritePNGFlags`, `ImwritePAMFlags`, `ImwriteWEBPLosslessMode`, `ImwriteHDRCompressionFlags`, `ImwriteBMPCompressionFlags`, `ImwriteGIFCompressionFlags` are capitalized, but `ImwriteTiffCompressionFlags`/`ImwriteTiffPredictorFlags`/`ImwriteTiffResolutionUnitFlags` use `Tiff`) — that inconsistency is inherited straight from `opencv2/imgcodecs.hpp`, not introduced on the C# side. Keep mirroring the C++ type name 1:1 regardless: it keeps the C# type grep-able against OpenCV's own headers/docs, which matters more than internal cosmetic consistency for a type name. This has always been this codebase's practice (`ImwriteEXRTypeFlags`/`ImwritePNGFlags`/`ImwritePAMFlags` pre-date this rule and already mirror C++ verbatim).
+
 ## Repository structure
 
 OpenCvSharp has three layers: