# Alloy Authors - Practical Alloy - Sequences (Highlights) ![rw-book-cover|256](https://readwise-assets.s3.amazonaws.com/static/images/article4.6bc1851654a0.png) ## Highlights - Sequences can only be used in fields, meaning they must be used as signature attributes. To declare an attribute that is a sequence, the keyword `seq` must be used, followed by the signature whose atoms can be contained in it. ([View Highlight](https://read.readwise.io/read/01jv5w9g3dnfnvgqe15w98jy8x)) ^889243568