The citation source code indicates the source of forward and backward citations. Values include the following:
| Source | Description |
|---|---|
| CH2 | Revealed during PCT Chapter 2 (preliminary examination) |
| SUP | Originates from the Supplementary Search Report |
| ISR | Originates from the International Search Report |
| APP | Cited by the applicant |
| SEA | Originates from the Search Report |
| 115 | Article 115 (observation by third parties) |
| EXA | Revealed during the examination phase (citing document is kind code "A") |
| OPP | Revealed during the opposition phase (only for B2 publications) |
| PRS | Origin pre-grant/pre-search (beginning week 13 of 2012 for US-A1 pre-grants) |
| APL | Filed for appeal by applicant/proprietor/patentee |
| FOP | Filed for opposition by any third party |
| TPO | Third party observation |
| UNKNOWN | Unknown source |