The documentation tells that the TAG field is NOT optional for the function type GAUSSIANFUNC.
However, this is not demonstrated in the samples given in the same page:
AtomPair CZ 20 CA 6 GAUSSIANFUNC 5.54 2.0 AtomPair CZ 20 CA 54 GAUSSIANFUNC 5.27 2.0 AtomPair CZ 20 CA 50 GAUSSIANFUNC 5.26 2.0 AtomPair CZ 20 CA 10 GAUSSIANFUNC 4.81 2.0 AtomPair CZ 20 CA 41 GAUSSIANFUNC 9.90 2.0
So if you copy and modify the sample file using GAUSSIANFUNC without TAG, and if you happen to have multiple lines of constraints, the line following the GAUSSIANFUNC line will be ignored since it will be read as TAG !!!
Just a heads up for users wondering why their constraints are not properly read in.