Updating from MEI 4 to MEI 5 adds mensural attributes

[rettinghaus]

Describe the problem
When loading a mensural file with version="4.0.0" into Verovio (updating it to MEI 5 effectively) every mensur element gets an @dot and @sign added automatically.

To Reproduce
Steps to reproduce the behavior:

1. Load "mensural-001.mei" from the test suite
2. Save it back
3. See error

Expected behavior
Non mandatory attributes shouldn't be added just by loading/updating a file. @dot and @sign are not required for mensur in MEI 5 and shouldn't be added (at least not without throwing a warning/info).

Input data
"mensural-001.mei" from the test suite

Verovio information

• Verovio 5.0.0
• all bindings