conditional variable assignment

[Haire, Don]

I have encountered some GNU make code with the following construction:

target_list: variable_name=variable_value

The intent appears to be the "conditional macro" idea that I have seen elsewhere, such that a rule which executes a target from this list will execute its commands in an environment where variable_name has the indicated value, even though that value might be different for targets not on the list.

However, I have found no documentation for the above syntax.  Is this a supported construction?

Thanks,
Don Haire