Returns a sequence containing the keys of its collection argument.
Although elements may be duplicated in a collection, keys, by their nature, must be unique; two different elements in a collection may not share a common key, even though distinct keys may yield identical elements.
The order in which the keys from collection appear in the key sequence is unspecified if collection is unstable under iteration. In particular, different calls to key-sequence with the same argument may yield differently ordered key sequences. If collection is stable under iteration, however, the resulting sequence of keys will be in the natural order for collection.
open
| collection | An instance of <collection>. |
| keys | An instance of <sequence> containing the keys of collection. |