======Expando substitutions======
Before a string can be used, it must be "expanded" whereby the expandos (things
that start with $) in the string are removed and replaced with their values, 
and backslashes (\\) are dequoted.  However, stuff inside of parenthesis 
"(...)" or curly braces "{...}" is considered literal text and is not 
expanded.  The stuff inside parenthesis and curly braces is usually
expanded later by someone else.

======Places where expandos are substituted======
The following strings are expanded each time they are used:
  - Command statements before they are executed, as in "//echo $ooga//"
  - The argument list to any function call, as in $foo(//$ooga//)
  - Any expression [[lval]]ue, as in "@//$ooga// += 3"
  - The contents of a [...] or "..." expression operand, as in "@foo = [//$ooga//]"
  - The default value of an arglist variable, as in "alias off (var1 default "//$ooga//") 
  - The width modifier in an expando (see below), as in "$[//$ooga//]foo"
  - The inside of the $(...) expando, as in $(//$ooga//)
  - The BX compatable form of $cparse(), as in $cparse("one two" //buckle my $1 shoes $ooga//)
  - The wildcard pattern of a flexible hook, as in /on msg '//$ooga// *' {...}
  - The word list to [[fe]] or [[fec]], as in /fe (//$ooga//) {...}
  - The word list to [[for|for var in]], as in /for i in (//$ooga//) {...}
  - The control value in [[switch]], as in /switch (//$ooga//) {...}
  - The matching pattern in [[switch]], as in /switch ($*) {(//$ooga//) {...}}
  - Ach, there are so many more...

=====Modifiers applicable to any expando=====

=====All forms=====

=====Protection from expansion=====

=====Expandos and expression mode=====

=====Special expandos=====