Comet parameter: digest_mass_range
         
         - Defines the mass range of peptides to search (based on MH+ or the singly
         protonated mass).
         
- This parameter has two decimal values.
         
- The first value is the lower mass cutoff and the second value is
         the high mass cutoff.
         
- Only spectra with experimental MH+ masses in within the defined
         mass ranges are searched.
         
- Valid values are two decimal numbers where the first number must
         be less or equal to the second number.
         
- The default value is "600.0 5000.0" if this parameter is missing.
         
Example:
         
digest_mass_range = 600.0 5000.0     search only 600.0 to 5000.0 mass range
         
digest_mass_range = 0.0 6500.0     search all spectra with peptide masses between 0.0 and 6000.0