A human-to-computer user interface is said to be "reactive" if it has the following characteristics: Reactivity was a major goal in the early user interface research at MIT and Xerox PARC.
A computer program which was not reactive would not be considered user friendly no matter how elaborate its presentation.
[citation needed] Early word-processing programs whose on-screen representations look nothing like their printer output could be reactive.
On-screen, it looked like a markup language in a character cell display, but it had deep built-in help which was always available from an on-screen menu bar, and the effect of each keystroke was obvious.
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