Add tags and inscription id documentation (ordinals#2351)

docs/src/SUMMARY.md

@@ -3,6 +3,7 @@
 - [Overview](overview.md)
 - [Digital Artifacts](digital-artifacts.md)
 - [Inscriptions](inscriptions.md)
+  - [Recursion](inscriptions/recursion.md)
 - [FAQ](faq.md)
 - [Contributing](contributing.md)
 - [Donate](donate.md)

docs/src/inscriptions.md

@@ -69,40 +69,59 @@ Content
 The data model of inscriptions is that of a HTTP response, allowing inscription
 content to be served by a web server and viewed in a web browser.
 
-Sandboxing
-----------
+Fields
+------
 
-HTML and SVG inscriptions are sandboxed in order to prevent references to
-off-chain content, thus keeping inscriptions immutable and self-contained.
+Inscriptions may include fields before an optional body. Each field consists of
+two data pushes, a tag and a value.
 
-This is accomplished by loading HTML and SVG inscriptions inside `iframes` with
-the `sandbox` attribute, as well as serving inscription content with
-`Content-Security-Policy` headers.
+Currently, the only defined field is `content-type`, with a tag of `1`, whose
+value is the MIME type of the body.
+
+The beginning of the body and end of fields is indicated with an empty data
+push.
+
+Unrecognized tags are interpreted differently depending on whether they are
+even or odd, following the "it's okay to be odd" rule used by the Lightning
+Network.
 
-Recursion
----------
+Even tags are used for fields which may affect creation, initial assignment, or
+transfer of an inscription. Thus, inscriptions with unrecognized even fields
+must be displayed as "unbound", that is, without a location.
 
-An important exception to sandboxing is recursion: access to `ord`'s `/content`
-endpoint is permitted, allowing inscriptions to access the content of other
-inscriptions by requesting `/content/<INSCRIPTION_ID>`.
+Odd tags are used for fields which do not affect creation, initial assignment,
+or transfer, such as additional metadata, and thus are safe to ignore.
 
-This has a number of interesting use-cases:
+Inscription IDs
+---------------
 
-- Remixing the content of existing inscriptions.
+The inscriptions are contained within the inputs of a reveal transaction. In
+order to uniquely identify them they are assigned an ID of the form:
 
-- Publishing snippets of code, images, audio, or stylesheets as shared public
-  resources.
+`521f8eccffa4c41a3a7728dd012ea5a4a02feed81f41159231251ecf1e5c79dai0`
 
-- Generative art collections where an algorithm is inscribed as JavaScript,
-  and instantiated from multiple inscriptions with unique seeds.
+The part in front of the `i` is the transaction ID (`txid`) of the reveal
+transaction. The number after the `i` defines the index (starting at 0) of new inscriptions
+being inscribed in the reveal transaction.
 
-- Generative profile picture collections where accessories and attributes are
-  inscribed as individual images, or in a shared texture atlas, and then
-  combined, collage-style, in unique combinations in multiple inscriptions.
+Inscriptions can either be located in different inputs, within the same input or
+a combination of both. In any case the ordering is clear, since a parser would
+go through the inputs consecutively and look for all inscription `envelopes`.
 
-A couple other endpoints that inscriptions may access are the following:
+| Input | Inscription Count | Indices    |
+|:-----:|:-----------------:|:----------:|
+| 0     | 2                 | i0, i1     |
+| 1     | 1                 | i2         |
+| 2     | 3                 | i3, i4, i5 |
+| 3     | 0                 |            |
+| 4     | 1                 | i6         |
 
-- `/blockheight`: latest block height.
-- `/blockhash`: latest block hash.
-- `/blockhash/<HEIGHT>`: block hash at given block height.
-- `/blocktime`: UNIX time stamp of latest block.
+Sandboxing
+----------
+
+HTML and SVG inscriptions are sandboxed in order to prevent references to
+off-chain content, thus keeping inscriptions immutable and self-contained.
+
+This is accomplished by loading HTML and SVG inscriptions inside `iframes` with
+the `sandbox` attribute, as well as serving inscription content with
+`Content-Security-Policy` headers.

docs/src/inscriptions/recursion.md

@@ -0,0 +1,27 @@
+Recursion
+=========
+
+An important exception to [sandboxing](../inscriptions.md#sandboxing) is recursion: access to `ord`'s `/content`
+endpoint is permitted, allowing inscriptions to access the content of other
+inscriptions by requesting `/content/<INSCRIPTION_ID>`.
+
+This has a number of interesting use-cases:
+
+- Remixing the content of existing inscriptions.
+
+- Publishing snippets of code, images, audio, or stylesheets as shared public
+  resources.
+
+- Generative art collections where an algorithm is inscribed as JavaScript,
+  and instantiated from multiple inscriptions with unique seeds.
+
+- Generative profile picture collections where accessories and attributes are
+  inscribed as individual images, or in a shared texture atlas, and then
+  combined, collage-style, in unique combinations in multiple inscriptions.
+
+A few other endpoints that inscriptions may access are the following:
+
+- `/blockheight`: latest block height.
+- `/blockhash`: latest block hash.
+- `/blockhash/<HEIGHT>`: block hash at given block height.
+- `/blocktime`: UNIX time stamp of latest block.