              Data items in the CHEM_COMP category give details (such as\
               name, mass, charge, etc.) about each of the chemical components\
               from which the relevant chemical structures can be constructed.\
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               The related categories CHEM_COMP_ATOM, CHEM_COMP_BOND, \
               CHEM_COMP_ANGLE, etc. describe the detailed geometry of these\
               chemical components.