b0298358_h_API___OCLC_Developer_Network__Description
[Parameter] frbrGrouping [Required?] optional [Possible Values] on, off default is on [Description] 
whether or not to use FRBR grouping which groups together similar editions and present only the top held record as the representative record for that group. This is sometimes referred to as a "FRBRized" result set. To see separate records for editions, set this parameter to "off".
Bibliographic Resource - WorldCat Search API | OCLC Developer Network