After working with InterSystems I was able to find what I was looking for by using the Matches function. The pattern I'm using is "1.N".
Shouldn't IsValidNumber appear as an option in the drop down list of the Expression Editor?
I was able to find what I needed. Set MSGX=##Class(EnsLib.HL7.Message).%OpenId(xxxxxxx) works
Log in or create a new account to continue