mechanicalturk - CrowdFlower: if-ony logic

Question

I am trying to set up a task in CrowdFlower using their CML language. I keep getting the following error with the only-if logic.

contains only-if logic that references a missing field

This is the code.

<cml:radios label="Is there any spoken text in the first audio or is the audio file empty?" class="" validates="required" instructions="Press the play button to play the audio in the above audio file. If you can't hear any audio please select the second option.">

<cml:radios label="Which option do you believe best answers the question" class="unmodified" only-if="is_there_any_spoken_text_in_the_first_audio_or_is_the_audio_file_empty?:[0]" validates="required"><cml:radio label="First option"/><cml:radio label="Second option"/><cml:radio label="Third option"/><cml:radio label="I would like to hear more options"/></cml:radios>

I've looked everywhere in their documentation but nothing seems helpful.

Answer 1

It turns out that the CML doesn't like quesionmarks ("?"). I used it in my label

<cml:radios label="Is there any spoken text in the first audio or is the audio file empty?" class="" validates="required" instructions="Press the play button to play the audio in the above audio file. If you can't hear any audio please select the second option.">

Once I removed it, there was no error.

Hope this helps someone.