Hello, according to the PDB format specification for chain IDs a chain ID can only consist of 1 (or 2) alphanumeric characters. I am wondering if there is a reason for this limitation since it seems to be more convenient to have chain IDs that are more descriptive than a single letter identifier. For example, if I have a multimer that contains multiple proteins that are identified as chains in the PDB, the only way to identify the proteins is to know their sequence length/ structure beforehand. This can be rather bothersome when using visualization software for analysis such as ChimeraX or for running a Python script to analyze crosslinks between specific proteins.