ISO/TS 10303-1291:2008 specifies the application module for
Plib class reference.

The following are within the scope of
ISO/TS 10303-1291:2008:

• the identification of a class in a library compliant to ISO 13584
  (Parts Library);
• items within the scope of application module External class, ISO/TS 10303-1275;
• items within the scope of application module External item identification assignment, ISO/TS 10303-1128;
• items within the scope of application module Person organization assignment, ISO/TS 10303-1013.