http://purl.org/tcl/home/man/tcl8.4/TkCmd/entry.htm

An entry box is designed to allow the user to enter one line of text
for use by the application.

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Hopefully, people will add new pages demonstrating various techniques for doing entry box validation of some common formats, like phone numbers, etc.

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See also:
   * [An entry with a history]
   * [Echo-free password entry]
   * [entryfield]
   * [Entry Field Processing]
   * [Entry Validation]
   * [Entry box validation for IP address]
   * [Integer entry validation with range check]
   * [Right-to-left entry widget]
   * [Time entry that never contains invalid data]
   * [Validating Credit Card Check Digits]
   * [Wcb]
   * [widget:entry]

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'''Programmable scientific calculator in two lines:''' (why, it can do ''asin'' and ''log'' ;-)
 pack [entry .e -textvar e -width 50]
 bind .e <Return> {catch {expr [string map {/ *1.0/} $e]} res; append e " = $res"} ;# RS
The [string map] forces floating-point calculation, so people won't be disappointed that 1/2 returns 0 ... See [A little calculator] for discussion.
And, as [CL] noted, this thingy is programmable: enter for example
 [proc fac x {expr {$x<2? 1: $x*[fac [incr x -1]]}}]
into the entry, disregard warnings; now you can do
 [fac 10]
and receive ''[[fac 10]] = 3628800.0'' as result...
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One common question is about "[Echo-free password entry]".
Entry has an easy answer:  its -show option is useful in
precisely this situation.

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