http://www.purl.org/tcl/home/man/tcl8.4/TclCmd/subst.htm
What's the use of subst? As Joe English, who has deep experience in the area, explains, "[subst] is massively handy in text-processing applications, especially SGML and XML down-translators. [subst] and [ string map] make Tcl particularly well-suited for this type of task." Many jobs for which Perl uses "right-hand-side" variables with regular expression substitution, Tcl does as REs whose results are subst-ituted.
Very simple example of using [subst] with XML/HTML.
set html {<html><head>$title</head></html>}
set title "Hello, World!"
set output [subst -nocommands $html]
set output
<html><head>Hello, World!</head></html>Another alternative would be to use XPath I use something like this in an application of mine. Of course the "text" of the 'html' variable above would probably come from a file.
I would much rather use XPath to hunt down the place to change.
RS most often uses subst for expanding Unicodes: cross-platform, in mostly 8-bit environments, it is most robust to output Unicodes in the \u.... notation - such snippets can be pasted into a text widget and visualized by
subst [$t get 1.0 end]
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