Consider deprecating old parsers API

**Problem**
When working with core, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

Start by locating the old parsers API and the core error-handling paths in the repository. Clarify which parser interfaces should be deprecated and which error messages need more detail; done requires an agreed deprecation scope and corresponding error-handling changes.

Written by the indexing model from the issue text.