Function external_instance_counts 

pub fn external_instance_counts(bytes: &[u8]) -> Option<HashMap<String, u32>>

How often a STEP assembly with external references places each referenced file (#247): the parts live in their own files ('bolt.stp'), the assembly file holds the structure. Which file a product definition stands for is read from

• DOCUMENT_FILE('bolt.stp', …) – the file (its id, or its name; a path is reduced to the file name), or the id of an APPLIED_EXTERNAL_IDENTIFICATION_ASSIGNMENT('bolt.stp', …, (#doc));
• linked to the definition by APPLIED_DOCUMENT_REFERENCE(#doc, …, (#definition)), PRODUCT_DEFINITION_WITH_ASSOCIATED_DOCUMENTS(…, (#doc)) or DOCUMENT_PRODUCT_EQUIVALENCE / …_ASSOCIATION(…, #doc, #product|formation|definition).

Every NEXT_ASSEMBLY_USAGE_OCCURRENCE below the top assemblies counts once for the file of its child; a child without a file of its own is a sub-assembly inside this file, whose occurrences count with its own multiplicity (depth bounded). File names in their original spelling; None when no occurrence leads to an external file (a monolithic STEP file, a single part, no STEP file).