tab in an input box

[Eduardo Viruena Silva]

For many years I have used several GUI, but I never have
learnt to include a "tab" char in an input box.

Tab char always changes the graphic item you are working with,
v. gr.  I'm using SquirrelMail to write this text.  If I
press "tab" the focus of my web browser  changes to the "send"
button.

Is it possible to include "tab" in an input box?
how?

Thanks in advance.

              Eduardo.