Problem/Motivation
The D8 CSS coding standards utilize underscores in CSS class names to designate sub-component classes. Underscores are replaced with hyphens when run through drupal_clean_css_identifier.
Proposed resolution
Remove "_" from the default filter array parameter on drupal_clean_css_identifier.
Remaining tasks
Needs patch.
User interface changes
N/A
API changes
This could potentially affect modules that rely on CSS class names being converted from underscores to hyphens, which could break styling.