6CYANA: read aco - CYANA command

Parameters: file=<filename>.aco            (required)
            type=<integer>                 (default: 1)
            append
            unknown=error|warning|skip     (default: error)

Reads an angle restraint file. Restraints that involve unknown residues
or angles can either cause an error, a warning, or can be skipped.
Optionally, the angle restraints are appended to those already present.
