IDX.DESCRIBERead an index declaration back: prefix, kind, type, fields, stored values, options, the table that compiled it, and the IDX.CREATE that recreates it.
| 语法 | IDX.DESCRIBE name |
| 分组 | index |
| 参数个数 | 2 |
| 起始版本 | 6.5.0 |
| 标志 | readonly, extension |
| 复杂度 | O(declaration size), plus O(tables) compiles to name the owning table; at the origin — the catalog is process-global |
| Redis 兼容性 | kevy-only |