Where a document cited in the search report may be useful for a better understanding of the principle or theory underlying the invention, or is cited to show that the reasoning or the facts underlying the invention are incorrect, it is indicated by the letter "T".
In the latter case, the "T" document constitutes evidence within the meaning of Art. 117(1)(c), rather than prior art within the meaning of Art. 54(2). Consequently, it is of no relevance whether a "T" document is published before or after the priority or filing date of the application being searched.
For example, the applicant claims a group of chemical compounds and the description gives a generically defined process for their production. The search division finds a document published after the priority date which clearly shows that the generically defined process is not able to produce all of the compounds covered by the claims. The search division may use this document to raise the objection that the claims are not supported by the description according to Art. 84 (see F‑IV, 6.3), and therefore it may cite this document as a "T" document.