Apple has filed a patent application for a keyboard that could display an infinite number of symbols on the key tops using organic light-emitting diodes (OLED), according to the U.S. Patent & Trademark Office's Web site.

Patent 20080001787, dubbed Dynamically Controlled Keyboard, outlines a keyboard whose keys would feature numerous OLEDs formed on a glass substrate that would also function as the key top. The OLEDs, perhaps in a 9-by-9 matrix, could be switched on or off, read the patent application, by software to morph the "display" on the faces of the keys.

Apple filed the application last March, but the Patent Office made it public only Thursday.

"One advantage is that keyboards and other peripherals are made much more user-friendly and the users' experience is enhanced, since there is a direct correspondence between what is displayed on the keyboard faces and the action that occurs when the corresponding keys are depressed," read the application. "This minimizes the users' need to memorize various keyboard layouts, for example, for different locales."

Such a keyboard, Apple said in the patent filing, could sport a traditional English QWERTY layout one moment, a Swedish-specific layout another and a Russian layout next. Or a specific program -- the patent application called out Adobe's PhotoShop -- could change the keys on-the-fly. "Whenever a user presses a function key or an auxiliary key, such as the Shift or the Ctrl key, the other keys on the keyboard change dynamically to display various tool functions that are activated by the function keys or auxiliary keys," said Apple.

Apple also claimed that an OLED keyboard's price could be "kept reasonably low since standard components used in conventional keyboards are largely used."

That might come as news to customers who have plunked down more than US$1,500 to be put on the wait list for the Optimus Maximus, an OLED-based keyboard designed by Moscow studio Art Lebedev. The stylish keyboard, originally scheduled to ship in November 2006, will now not be available until the end of February because of a shortage of Philips microprocessors.