add NIP-50 query extension

50.md

@@ -26,11 +26,50 @@ Relays SHOULD interpret the query to the best of their ability and return events
 Relays SHOULD perform matching against `content` event field, and MAY perform
 matching against other fields if that makes sense in the context of a specific kind. 
 
-Results SHOULD be returned in descending order by quality of search result (as defined by the implementation),
-not by the usual `.created_at`. The `limit` filter SHOULD be applied after sorting by matching score.
 A query string may contain `key:value` pairs (two words separated by colon), these are extensions, relays SHOULD ignore 
 extensions they don't support.
 
+### Query Expression Extensions
+
+Relays MAY support query expressions with boolean operators and filter attributes. When supported, this MUST be advertised in NIP-11:
+
+```json
+{
+  "supported_nips": [50],
+  "nip50_search": {
+    "boolean_operators": true,
+    "filter_attributes": ["limit", "since", "until"]
+  }
+}
+```
+
+When `boolean_operators` is `true`, relays SHOULD support:
+
+- Terms split by whitespace (implicit AND)
+- Double quotes for phrase matching: `"hello world"`
+- Boolean operators: `AND`, `OR` (uppercase, case-sensitive)
+- Parentheses for grouping: `(cat AND dog) OR bird`
+- Operator precedence: `AND` binds tighter than `OR`
+
+Examples:
+- `hello world` → both terms required (implicit AND)
+- `hello OR world` → either term matches
+- `cat AND (dog OR bird)` → "cat" plus either "dog" or "bird"
+
+When `filter_attributes` is present, relays SHOULD support filter attributes in the query string:
+
+- `limit:<number>` - limit number of results (e.g., `limit:50`)
+- `since:<unix timestamp>` - filter events after timestamp (e.g., `since:1609459200`)
+- `until:<unix timestamp>` - filter events before timestamp (e.g., `until:1640995200`)
+
+Examples:
+- `nostr limit:50` → search "nostr" and return up to 50 results
+- `bitcoin since:1609459200` → search "bitcoin" for events after the specified time
+- `cats OR dogs limit:100 since:1640995200` → combined query with filters
+
+Results SHOULD be returned in descending order by quality of search result (as defined by the implementation),
+not by the usual `.created_at`. The `limit` filter SHOULD be applied after sorting by matching score.
+
 Clients may specify several search filters, i.e. `["REQ", "", { "search": "orange" }, { "kinds": [1, 2], "search": "purple" }]`. Clients may 
 include `kinds`, `ids` and other filter field to restrict the search results to particular event kinds.