+/**
+ * A user-defined input mode binding of a typed string to an automatically
+ * inserted expansion string.
+ *
+ * Abbreviations have a left-hand side (LHS) whose text is replaced by that of
+ * the right-hand side (RHS) when triggered by an Input mode expansion key.
+ * E.g. an abbreviation with a LHS of "gop" and RHS of "Grand Old Party" will
+ * replace the former with the latter.
+ *
+ * @param {[Mode]} modes The modes in which this abbreviation is active.
+ * @param {string} lhs The left hand side of the abbreviation; the text to
+ * be replaced.
+ * @param {string|function(nsIEditor):string} rhs The right hand side of
+ * the abbreviation; the replacement text. This may either be a string
+ * literal or a function that will be passed the appropriate nsIEditor.
+ * @private
+ */