https://issues.jenkins-ci.org/browse/JENKINS-48523  added support to the tag when condition with the comparator. 

At the moment, the branch when condition does support GLOB, but no REGEXP patterns. Let's standardize the branch condition format as done with the tag condition.

when {
    branch "release-*"
}
when {
    branch pattern: "release-*", comparator: "GLOB"
} 
when {
    branch pattern: "release-\\d+", comparator: "REGEXP"
}