I'm writing some kind of IFF file browser
https://github.com/mattrust/iffmaster

Can I assume that data chunk IDs are generic?
E.g. ABCD

Or would it be better to check it with the parent's chunk sub ID?
E.g. ILBM.ABCD, 8SVX.ABCD ...

The latter would be more work, because e.g. ILBM and ACBM share almost the same data chunk IDs.

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AROS - Make code not war

@Mazze

My recollection was that sub-chunk ids aren't generic across different iff types; though as you've seen they can be specified that way where useful to do so.

But I also checked with ChatGPT seeing that is only a recollection...

In the Amiga IFF (Interchange File Format) documentation, you would typically find the explanation about sub-chunk IDs and their specificity to particular data chunks in sections that describe the structure of chunks and sub-chunks in detail. Specifically, this explanation can often be found in the section discussing the chunk structure, chunk IDs, and sub-chunks.

To summarize the key points that are relevant to your question:

IFF files are organized into chunks, where each chunk has a four-character ID (also known as a fourcc) that identifies its type.
Some chunks may contain sub-chunks, which are additional data elements nested within the main chunk.
Sub-chunk IDs are not standardized across different chunk types. This means that the ID used for a sub-chunk within one chunk type (e.g., the "FORM" chunk) may differ from the sub-chunk IDs used in another chunk type (e.g., the "ILBM" chunk, which is a specific chunk for bitmap data).
This principle is typically mentioned in the chunk type specifications and the format-specific sections of the documentation (e.g., for image files, sound files, etc.). The format is flexible, and sub-chunks' meanings depend on the context of their parent chunk. The IDs for sub-chunks are assigned according to the specific data structure or use case for that chunk type.

In terms of documentation structure, you'd be looking for sections with titles like:

"Chunk structure"
"Sub-chunks"
"Chunk type definitions"
"Chunk ID usage"
For example, in a formal specification of the IFF format, you would find a section where chunk IDs are defined, followed by a description of how different chunks may include sub-chunks with different IDs, and the significance of those IDs is explained in the context of the parent chunk's data.

If you're working with a specific application of IFF (like the ILBM format for images), look in the format-specific sections where sub-chunks for that format are detailed, and you'll see how the sub-chunk IDs are defined and used uniquely within that chunk type.