Richard Suchenwirth 2002-11-22 - In real life, "entity" is a rather vague term for things or beings. In XML, it stands for strings marked up between "&" and ";", e.g.
>
is equivalent to the "greater" sign, >. In Tcl, variable names prefixed with $ do string substitutions, even inside another string (if not braced). Consider this example, where initially two "entities" are defined - the trailing list produces an empty string and hence removes traces of the embedded commands; further down the text, the variables are indeed replaced with their assigned values:
% set t "[set h Humpty-Dumpty;
set k king; list]
$h sat on a wall,
$h did a great fall,
all the $k's horses and all the $k's men
couldn't put $h together again."
% puts $t
Humpty-Dumpty sat on a wall,
Humpty-Dumpty did a great fall,
all the king's horses and all the king's men
couldn't put Humpty-Dumpty together again.One of the rare cases where a sequence of statements inside the [] brackets makes (some) sense... The practical use is to make substrings that occur more than once configurable in one place.
Shorter example:
subst {[set ht "[set h {Happy Birthday}] to you"],$ht,$h dear XX,$ht}