CR — Timerevent based on data not possible

According to the specification, a timereventlistener can have a timerexpression (ISO-8601 format) and a starttrigger (event).

What I seem to be missing here is the following:
In the data of a case, I can enter a date (e.g. in a certain task). I would like to set the timer to trigger at the date (or duration) specified in the data.

This does not seem possible when following the specification. Only a fixed time or duration can be entered.

*Modify table 5.13 attribute timerExpression to be of type Expression *

1. The timerExpression attribute in Figure 5.5 should be defined as follows

timerExpression : Expression
with the following text

"An expression that MUST evaluate to an ISO-8601 conforming representation for date, time, duration or interval."

2. We need to modify the metamodel and add an Expression class right to TimerEventListener and timerExpression becomes an association from TimerEventListener to Expression