ATTRIBUTE [DELETE] repeat(word)
The ATTRIBUTE command is used to specify residue attributes. Each word following the ATTRIBUTE command is added to the residue attribute list, unless the DELETE option is specified. In that case, the words are deleted from the residue attribute list.
At present, the only residue attribute that has any significance is the D attribute, which informs the conformational search code, see Conformational Search, that the residue is a D amino acid, and should be processed accordingly.