A regular expression to disable or prohibit selection of specific branches (e.g. (master|main) or release/.*).

Behavior: Branches matching this pattern will still appear in the dropdown list for visibility, but will be grayed out and disabled (marked with (disabled)), preventing users from selecting them.

Security: If custom branch input is enabled, users cannot bypass this rule by manually typing a disabled branch name. Submissions matching this pattern will be rejected.

Examples:

• master - Disable the master branch
• (master|main) - Disable both master and main branches
• release/.* - Disable all release branches
• deprecated-.*|archive/.* - Disable deprecated or archived branches