Refactor parsers for better readability

**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 core parser and error-handling entry points mentioned in the issue, then review how current failures are reported. The work is done when parser errors provide more descriptive messages and the resulting behavior can be verified for representative failures.

Written by the indexing model from the issue text.