Man pages matching name tcl_decrrefcount in section 3tcl:

Tcl_DecrRefCount.3tcl.en	debian 10 / tcl8.6-doc
Tcl_DecrRefCount.3tcl.en	debian 11 / tcl8.6-doc
Tcl_DecrRefCount.3tcl.en	debian 12 / tcl8.6-doc