drIsWaveform Function

Hello,

I am trying to find out if the evaluation of a expression is a waveform or a scalar type.

For example:

  myExpression = "dB20(VF(\"/sig_out\"))"

  eval = car(errsetstring(myExpression))

I would like to have a function that returns t or nil depending on whether eval is a waveform or a scalar. 

I read from the following post, that the drIsWaveform should do exactly what I want:

  http://www.designers-guide.org/Forum/YaBB.pl?num=1141952888

However unlike in this post, the evaluation of my expression returns: srrWave: =XXX instead drwave=XXX

so that  drIsWavefirm(eval) returns the wrong value (nil in this case)

My question:

1) Why do I get a srrWaveform instead of a drWaveform?

2) What is the difference between both types?

3) is there any documentation related to the different data structures used in ADE? 

Many Thanks for your help.

Driss