The general idiom for this is not to attach to PreferencesManager.ready, but rather to define the preference and add a listener for preference changes [as in this kitchen sink example](https://github.com/mackenza/brackets-kitchen-sink/blob/ee68d173d6e0b4ba687cb2ffa62c1ace3dbc5250/main.js#L108). That way, if the preference changes because the user edits it by hand or some mythical preferences UI, you'll have the up to date value.

Note that the event that comes in just says that the pref *may* have changed and you need to retrieve the value and act accordingly.