Systems and methods for streaming content are disclosed. A Media Presentation Description (MPD) may be associated with streaming content, for example, in Dynamic Adaptive Streaming Over HTTP (DASH). An MPD may comprise an element, e.g., a header element or URL query element, which provides a name/value functionality. An element may allow a request that results in insertion of custom headers. Requests may be used for retrieval of a subsegment, segment, or MPD, re-referencing of remote elements, or triggered by an event. The event may be embedded either in an MPD or in segments.