Key-value sequences are intended for handling data that is accessed by one or more key, like a card index. They repurpose various sequence features originally designed for text sequences to offer reasonable performance via a convenient interface.
Key-value sequences, like all sequences, have a unique id. It is also possible to query the number of entries. Tags work as for text sequences.
An entry is a block by another name. Entries can be filtered by primary and secondary keys and by content. The fields of each entry are exposed as item groups.
See the full schema for key-value sequences for more details.