I have tried the following regexes. {startTime:[01]?[0-9]|2[0-3]:[0-5][0-9]} {startTime:[0-9]+} -- not a time of course, but thought I would give it something easy {startTime:"[0-9]+"} just {startTime} works When a regex is present , I get errors like: [9] Unable to expand: Beer *List* Unknown BLone BLone 25-Feb-2014 startTime 25-Feb-2014 endTime [ERR 102] Line 9:8 mismatched input '*List*' in rule "a" DSL lookes like [when]Beer *List* {x} {y} ... {startTime[0-9]+} ... =eval($foo.doThis("{x}", "{y}", ..., "{startTime}, ...")) -- View this message in context: http://drools.46999.n3.nabble.com/6-0-1-F-Regex-validation-in-DSL-causes-... Sent from the Drools: User forum mailing list archive at Nabble.com.