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From WCAG WG
WCAG definition of keyboard interface
interface used by software to obtain keystroke input
Note 1: A keyboard interface allows users to provide keystroke input to programs even if the native technology does not contain a keyboard.
Example: A touchscreen PDA has a keyboard interface built into its operating system as well as a connector for external keyboards. Applications on the PDA can use the interface to obtain keyboard input either from an external keyboard or from other applications that provide simulated keyboard output, such as handwriting interpreters or speech-to-text applications with "keyboard emulation" functionality.
Note 2: Operation of the application (or parts of the application) through a keyboard-operated mouse emulator, such as MouseKeys, does not qualify as operation through a keyboard interface because operation of the program is through its pointing device interface, not through its keyboard interface.
Additional guidance when applying to Electronic Documents and Software Aspects of Products
This applies directly as written, and as described in WCAG 2.0 glossary.
We draw the readers' attention to the note in SC 2.1.1 that uses this definition and which reads:
This does not imply that software must directly support a keyboard or "keyboard interface". Nor does it imply that software must provide a soft keyboard. Underlying platform software may provide device independent input services to applications that enable operation via a keyboard. Software that supports operation via such platform device independent services would be operable by a keyboard and would comply.