PatternVariableBuilder can be extremely inefficient in some cases

When org.jbehave.core.steps.PatternVariantBuilder#variantsFor is called, the following regex is used -

 "(.*?)?(\\{((.*?)(\\|)?)*?\\})(.*)"

.
Matching with this regex can be very lengthy and CPU intensive when there is an unmatched curly bracket for example, like here:

create entity of type $entityType {set properties $propertyNames to values $propertyValues