The file tcl.h should be considered a public declaration of the Tcl C functions, defines/macros, and structures which a developer can safely depend on. (Some extensions also use things from tclInt.h, but the price for that is that they require more maintenance in order to keep working. Stick with tcl.h as long as possible.) Most of the actual function declarations are found in the tclDecls.h file; this has to do with the Stubs mechanism.
LV When I look in tcl.h, I see only 3 functions listed, along with 2 tcl related #include lines - tclDecls.h and tclPlatDecls.h. Is it correct to assume that any function declared as EXTERN in these two additional files are also considered a part of the public API for Tcl?
Tcl C API functions include:
[A list by topic (where related functions are collected together) should be more useful, as the HTML docs already provide this kind of alphabetic list.] [Feel free to organize data on the wiki in the way that helps you most - or seems to be most helpful.]
with the following APIs having their own pages here on the wiki:
See also Tcl API and the references there. See also Tcl/Tk 8.5: New public C routines