PD4ML supports dynamic placeholder $[var] substitution with pd4ml.setDynamicParams() API call. (note the square brackets!)

Do you try to use ${test.src} with pd4ml.setDynamicParams()? I am afraid it does not work.

If it is about a more general use of Expression Language, please make sure the EL elements are resolved before the HTML is passed to PD4ML. PD4ML does not process EL by itself.