<div>
<p>Return value from Groovy script is treated as Label Expression. It is treated as followings:</p>
<ul>
    <li>A non-string value will be converted to a string using toString()</li>
    <li>When null or blank string is returned, node restriction does not take effect (or is not overwritten).</li>
    <li>When exception occurred or Label Expression is not parsed correctly, builds are canceled.</li>
</ul>
<br>
<p>Following variables are binded, but there may be cases that some type of parameters are not set, or set to wrong value.
This is for a build is not started yet when this Groovy script is evaluated.</p>
<ul>
    <li>Parameters specified in "This build is parameterized"</li>
    <li>Axes defined in a matrix project.</li>
    <li>Other variables that plugins create.</li>
</ul>
<br>
<p>Here is an example:</p>
<code style="white-space: pre-wrap;">
Example1-----------------------------------------------------------------------------
// parameters defined in "This build is parameterized" are binded,
// and you can use them just as variables.
if(is_test == "true")
{
    // use nodes labeled "debug_node"
    return "debug_node";
}
// returning blank value does not restrict nodes.
// When restricted with other parameters or plugins, that configuration will be used.
return null;

Example2-----------------------------------------------------------------------------
// Values defined with axe with a matrix project are also binded.
// But that value is not defined in a root matrix build, 
// so access with binding.getVariables().get(VARNAME) .
// (accessing VARNAME directly results exceptions)
switch(binding.getVariables().get("target"))
{
    case "Win32":
    case "Win64":
        // run on Windows.
        return "Windows";
    case "Linux32":
    case "Linux64":
        // run on Linux.
        return "Linux";
}
</code>
</div>