Keyworkd "collections" and "participant" are not recognized on the syntax plantuml for the version 1.2019.3
when i write
I have this message
Did you mean :
And it's the same for collections.
It's ok for keywords actor, control, boundary, database.
I have found the error : i use lef to right direction option, when i delete this, participant and collections are recognized. This option mustn't be used for this type of diagram :-D