A global array created by Tcl on startup, where keys hold proc names, and the value is a script indicating how to make the key-named proc available (typically source
with full pathname of a Tcl file). Tcl initialises the array by sourcing tclIndex
files. See the library
manpage for more.
For finding the location of the source for auto_load
ed commands, this array is very useful. E.g., for parray