docs(build): say that search finds a file by its extracted text

content/docs/build/handle-files.mdx

@@ -104,6 +104,23 @@ A write that names another hash in `blob_ref`, such as one copied from elsewhere
 
 A hash in any other property, such as an image link in a note's body, is text: the write is taken and the hash lends nothing.
 
+## Find a file by its text
+
+Once the housekeeping job has written a file item's `extracted_text`, [search](/build/list-filter-search#search) finds the file by any word in it:
+
+```bash tab="CLI" tab-group="client"
+marfa search quokka --type core.file
+```
+
+```http tab="HTTP"
+GET /search?q=quokka&type=core.file
+Authorization: Bearer <key>
+```
+
+The job runs every 30 seconds by default, so a new file is found by its `title`, `description` and tags first and by its text a little later. Search matches only the text the job kept, which [`MARFA_ENRICHMENT_MAX_TEXT_CHARS`](/run/settings) limits. A file in the bin is never found. A device that holds the file finds it by its text once it has fetched the item with its `extracted_text`, which it does when it next catches up.
+
+Enrichment is on unless the [settings](/run/settings) switch it off, and an image has text only while OCR is on.
+
 ## Download the bytes
 
 [Download a blob](/api-reference/blobs/downloadBlob) answers the bytes as they were uploaded:

content/docs/build/list-filter-search.mdx

@@ -173,6 +173,8 @@ Each entry in `data` holds the `item`, its `metadata`, a `relevance_score`, and
 
 Put a query in double quotes to match a phrase. A search takes a listing's parameters too, such as `type`, `tags` and `filter`.
 
+Search also reads the text of a file. After the `enrichment-sweep` job has read a file item's bytes and written its `extracted_text`, a search finds the file by any word in that text, as it finds any other `string` field, on the server and in a copy on a device. Until then, a search finds the file only by its other fields and tags. See [Handle files](/build/handle-files#find-a-file-by-its-text).
+
 ## Count items
 
 [Get item counts](/api-reference/items/getItemStats) counts the items a listing would match, by state or, with `by=type`, by type:

content/docs/catalog/items.mdx

@@ -13,4 +13,4 @@ Search always reads these fields where they hold a `string` ([`search-and-filter
 
 <include cwd>src/generated/catalog/searched-field-names.md</include>
 
-It also reads every other `string` field a type declares or inherits, unless the field sets `searchable` to `false`, and an item's tags. [List, filter and search](/build/list-filter-search#search) shows how to search.
+It also reads every other `string` field a type declares or inherits, unless the field sets `searchable` to `false`, and an item's tags. That includes a file item's `extracted_text`, the text Marfa reads from the file's bytes. A type that inherits a file type can't set `searchable` to `false` on it. [List, filter and search](/build/list-filter-search#search) shows how to search.