Fluffy clouds are your friends

In early iterations of the design, it is better to get a breadth-pass than to get bogged down in the depth of one particular detail.  Use fluffy clouds - unashamedly - to communicate that you simply don't know what will appear in that part of the design yet.  Better this approach than detailing an ill-thought out guess which might cause the kernel of a good idea to be tossed into the chaff-pile by a stakeholder with a critical eye for detail.