If I have relation between 2 "container rectangles", then the formating is ignored and written as normal text (=.. does not activate header1) like in following sample
(AnotherNode -> ParentNode : "=Format NOT working" should be formated too)
@startuml
rectangle "Parent Node" as ParentNode {
rectangle "Inner App" as InnerApp
}
rectangle "Another Node" as AnotherNode{
rectangle "Another App" as AnotherApp
}
AnotherNode -> ParentNode : "=Format NOT working"
AnotherApp -> InnerApp : "=Format working"
AnotherApp -> ParentNode : "=Format working"
AnotherNode -> InnerApp : "=Format working"
@enduml
http://www.plantuml.com/plantuml/uml/VOun2i9044NxFSLdUoyWAAOHRDJ22oncY68o6yOL2_7kJjOmJ9NjtlBcyOMk9N7N4-8v2N71CRSKaPxuyuJu1EXpxe6P1CquLhEIGlY6uAI6SxcfPiNvOs9VzB8rArlLNMArzTFMY9jzbY7fyjC5xooFEtTHJooW5pRH--PwrSSNP9ko6DuHjw-X_m40