Emacspeak: An Overview Of Voice-Lock Over The Years

Audio formatted output is provided via voice-lock in Emacspeak. The feature was originally implemented in 1994 and significantly overhauled in 2002 (with no change in functionality). Now, in 2015, the implementation has been reworked to be once again simpler — but with the same functionality.

Font-lock was a new feature in Emacs 19 — it was introduced right around the time the Emacspeak project was started. At the time, there were multiple font-lock packages in Emacs. Emacspeak implemented voice-lock via a stand-alone module that attached property personality to buffer contents. The dtk-speak Text-To-Speech module treated strings annotated with property personality as an aural display list when producing spoken output.

In the winter of 1995, I implemented Aural CSS in emacspeak, and this resulted in module acss.el — that module provides a clean abstraction for defining values that can be assigned to property personality. Next, the rest of emacspeak was overhauled to express all voice-lock features via the ACSS abstraction.

With feature font-lock now mature, Emacs itself converged on a single font-lock module with jit-lock.el providing just-in-time font locking. This meant that Emacspeak's voice-lock feature could now be more easily implemented by attaching appropriate advice to lisp functions put-text-property and friends — this led to the deletion of module voice-lock.el and the creation of module emacspeak-personality.el.

That module provided multiple options for how faces were mapped to personalities:

• Cumulative where property personality was either appended or prepended to the list of personalities at any given position.
• Simple: where the new personality directly replaced any previously applied personality property.
• None: Where faces were not mapped to personalities.

And now, in 2015, the code in module dtk-speak.el that implements audio-formatting has been overhauled to directly map faces to personalities. This implementation can be enabled by setting the option emacspeak-personality-voiceify-faces provided in module emacspeak-personality.el to All. This means that the new implementation can co-exist (at least for a while) with the earlier advice-based implementation from module emacspeak-personality.el.

once deemed to be stable, the new implementation will become the default — by changing the default value of emacspeak-personality-voiceify-faces to none.

From an end-user's perspective, nothing has changed in 21 years. From the perspective of implementing voice-lock for Emacs modules, nothing has changed — all that an Emacspeak extension for a specific package needs to do to enable voice-lock is to set up a face->personality mapping as before via function voice-setup-add-map. Note that property personality will continue to have higher precedence than property face with respect to the audio formatting that gets applied i.e. Emacspeak first consults value of property personality, and if that is not set, but there is a face property set, then that face->personality mapping (if defined) is used as the aural style.