Many development methodologies specify that requirements are locked down at the beginning of a project. Although that is not the case in Agile, it does not mean that requirements are loosey-goosey! The advantage of Agile and its short iterations is that it is easy to quickly recognize that work is not progressing as desired what the customer asked for. If it is not what they wanted then the requirements must be changed. Team members should be able to handle such changes on an Agile project. It shouldn’t be so tied to code, a story card or any other component of work that prevents providing a solution which meets the customer’s needs. The general idea is that requirements can change a lot at the beginning of the release, and very little at the end.