This variable identifies whether or not the tcl interpreter
is operating in interactive mode or not.  If its value is 1 ,
then the interpreter acts as if it were an interactive interpreter. See [tclsh] for a list of the
differences between interactive and non-interactive mode.

[Ro] You can shorten commands in interactive mode, e.g.: "inf" for "info". - [RS] Yup - and this is especially delightful on a [PocketPC] where less stylus-tapping is better. If the abbreviation is unambiguous, like ''ll'' for [llength], it saves time and screen space; if it is ambiguous (e.g. 'l'), it is another [introspection] helper - the educational error message shows you the possible completions, just as [[info command l*]] would have done. Funny though, in my sandbox on W95/Tcl 8.4.5 it doesn't work :(

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[Tcl syntax help]