A Java regular expression matched against the full branch name. The pattern must match the entire name (as if surrounded by ^ and $).

Examples:

• main|develop – matches only main and develop
• release/.* – matches all release branches
• feature/.* – matches all feature branches
• (?!feature/).* – matches everything except feature branches (negative lookahead)
• .* – matches everything (same as "All branches" mode)

If the pattern is syntactically invalid, it is treated as matching all branches and a warning is written to the Jenkins log.