TEA or Tcl Extension Architecture is a series of recommendations for extensions written on at least the Unix platform (hopefully developers for non-Unix operating systems contribute tools, enhancements, etc. so that one set of source can be used across all the platforms...).
TEA is more of a set of utilities for developing extensions than a single standard for "the right way to do extensions". TEA offers a set of guidelines, and aspires to become a reference for best practices, but there is room for improvement and, indeed, alternatives. Tcl provides the basic [load] and [source] facilities, and there are many ways to effectively use those facilities "extend" Tcl.
./configure \ --with-tcl=/path/to/tcl \ --with-tclinclude=/path/to/tcl/include \ --prefix=//d/progra~1/tcl make make install