1. A computer implemented method for modifying a grammar of a hierarchical multimodal menu comprising a plurality of tiers including a higher tier and a lower tier in a voice-enabled computing environment, the method being performed by at least one computer of the voice-enabled computing environment and comprising: in response to receiving a first speech input from a user while the user is navigating the menu at the higher tier, comparing the first speech input to commands of a limited higher-tier grammar associated with the higher tier, the limited higher-tier grammar including commands that can be invoked when the user is navigating at the higher tier and cannot be invoked when the user is navigating at least one other tier of the hierarchical multimodal menu; monitoring the user invoking a speech command of a limited lower-tier grammar associated with the lower tier, the limited lower-tier grammar including commands that can be invoked when the user is navigating at the lower tier, wherein the speech command is associated with an action; and adding the speech command to the limited higher-tier grammar in dependence upon the frequency of the user invoking the speech command such that when the user subsequently navigates the menu at the higher tier, the speech command added to the limited higher-tier grammar from the limited lower-tier grammar may be invoked at the higher tier.