An increasing number of distributed applications will be written for mobile hosts, such as laptop computers, third generation mobile phones, personal digital assistants, watches and the like, with focus on peer-to-peer collaboration. Application engineers have to deal with a new set of problems caused by mobility, such as low bandwidth, context changes or loss of connectivity. During disconnection, independently from each others, users will typically update local replicas of shared data, possibly generated by peers. The resulting inconsistent replicas need to be reconciled upon re-connection. To support building mobile applications that use both replication and reconciliation over ad-hoc networks, we have designed XMIDDLE, a peer-topeer middleware that targets mobile computing settings. In this paper we describe XMIDDLE and give a flavour of how reflection capabilities are used to allow application engineers to influence replication and reconciliation techniques. XMIDDLE enables the transparent sharing of XML documents across heterogeneous mobile peers, allowing on-line and off-line access to data.