title: Nuke ChannelMask_Knob required argument
body: <p>I am trying to figure out what the required string argument for the nuke.ChannelMask_Knob() function corresponds to. On some other knob constructors the first argument seems to be the name/label, but that does not seem to be the case for the ChannelMask_Knob...</p>
  
  <p>I have looked at the Nuke Python API, but I am unsure how to follow it back to the appropriate function definition to answer my question. My line of thinking is that this has to do with the <strong>init</strong> function which is overridden by the ChannelMask_Knob class, but the parameter list according to the API is just "..." which I believe means it has to do with a builtin function. Since I can't see the body of the <strong>init</strong> function, I have no idea what that argument is used for, thus my problem...</p>
  
  <p>Here is an example of my issue:</p>
  
  <pre><code>test_knob = nuke.ChannelMask_Knob("required_argument")
  node.addKnob(test_knob)
  </code></pre>
  
  <p>This works just fine, but I would like to know what the "required_argument" is used for since it is apparently not the name or label for the knob.</p>