Add image tags and change format of the price tag.

402.md

@@ -25,6 +25,7 @@ The `.pubkey` field of these events are treated as the party creating the listin
 ### Metadata
 
 - For "tags"/"hashtags" (i.e. categories or keywords of relevance for the listing) the `"t"` event tag should be used, as per [NIP-12](https://github.com/nostr-protocol/nips/blob/master/12.md).
+- For images, whether included in the markdown content or not, clients SHOULD use `image` tags as described in [NIP-58](https://github.com/nostr-protocol/nips/blob/master/58.md). This allows clients to display images in carousel format more easily.
 
 The following tags, used for structured metadata, are standardized and SHOULD be included. Other tags may be added as necessary.
 
@@ -32,7 +33,17 @@ The following tags, used for structured metadata, are standardized and SHOULD be
 - `"summary"`, for short tagline or summary for the listing
 - `"published_at"`, for the timestamp (in unix seconds – converted to string) of the first time the listing was published.
 - `"location"`, for the location.
-- `"price"`, for the price of the thing being listed. This is a free-form string. e.g. `€2,000/week` or `$22 per hour` or `$500`
+- `"price"`, for the price of the thing being listed. This is an array in the format `[ "price", "<number>", "<currency>", "<frequency>" ]`.
+  - `"price"` is the name of the tag
+  - `"<number>"` is the amount in numeric format (but included in the tag as a string)
+  - `"<currency>"` is the currency unit in 3-character ISO 4217 format.
+  - `"<frequency>"` is optional and can be used to describe recurring payments.
+
+#### `price` examples
+
+- $50 one-time payment `["price", "50", "USD", ""]`
+- €15 per month `["price", "15", "EUR", "monthly"]`
+- £50,000 per year `["price", "50000", "GBP", "yearly"]`
 
 Other standard tags that might be useful.
 
@@ -51,9 +62,10 @@ Other standard tags that might be useful.
     ["title", "Lorem Ipsum"],
     ["published_at", "1296962229"],
     ["t", "electronics"],
+    ["image", "https://url.to.img", "256x256"],
     ["summary", "More lorem ipsum that is a little more than the title"],
     ["location", "NYC"],
-    ["price", "$100"],
+    ["price", "100", "USD"],
     [
       "e",
       "b3e392b11f5d4f28321cedd09303a748acfd0487aea5a7450b3481c60b6e4f87",