Query: What is supposed to happen with multiple <materialx> tags in a document ?

## Query

I just accidently came across this. But if you have multiple `` blocks what is supposed to occur ?

Currently it will just read the first block and discards subsequent blocks without any error / warning.
A trivial thing, (and assume it's just how the parser works?) but users may become confused if some content does not read in.

Start by tracing the C++ parser path that handles multiple blocks and inspect any existing parser tests or documentation. First establish the intended behavior for repeated blocks; done should include a documented decision, appropriate handling of subsequent blocks, and regression coverage for the case described.

Written by the indexing model from the issue text.