Is it possible to use <camunda:string> in <bpms:process>

Is it possible to use camunda:string in bpms:process
Because we need to store a long String (usually json) in the bpmn file as a global custom attribute of the process, and use it in some parts of the process (delegate, listener)
I try to use as follows

But I didn’t find a way to get the text content, so can you guys give some advice
thank you very much