Add inscription docs (#994)

docs/src/SUMMARY.md

@@ -1,6 +1,7 @@
 # Summary
 [Introduction](introduction.md)
 - [Overview](overview.md)
+- [Inscriptions](inscriptions.md)
 - [FAQ](faq.md)
 - [Contributing](contributing.md)
 - [Guides](guides.md)

docs/src/inscriptions.md

@@ -0,0 +1,64 @@
+Inscriptions
+============
+
+Inscriptions inscribe sats with arbitrary content, creating bitcoin-native
+digital artifacts, more commonly known as NFTs. Inscriptions do not require a
+sidechain or separate token.
+
+These inscribed sats can then be transferred using bitcoin transactions, sent
+to bitcoin addresses, and held in bitcoin UTXOs. These transactions, addresses,
+and UTXOs are normal bitcoin transactions, addresses, and UTXOS in all
+respects, with the exception that in order to send individual sats,
+transactions must control the order and value of inputs and outputs according
+to ordinal theory.
+
+The inscription content model is that of the web. An inscription consists of a
+content type, also known as a MIME type, and the content itself, which is a
+byte string. This allows inscription content to be returned from a web server,
+and for creating HTML inscriptions that use and remix the content of other
+inscriptions.
+
+Inscription content is entirely on-chain, stored in taproot script-path spend
+scripts. Taproot scripts have very few restrictions on their content, and
+additionally receive the witness discount, making inscription content storage
+relatively economical.
+
+Since taproot script spends can only be made from existing taproot outputs,
+inscriptions are made using a two-phase commit/reveal procedure. First, in the
+commit transaction, a taproot output committing to a script containing the
+inscription content is created. Second, in the reveal transaction, the output
+created by the commit transaction is spent, revealing the inscription content
+on-chain.
+
+Inscription content is serialized using data pushes within unexecuted
+conditionals, called an "envelopes". Envelopes consist of an `OP_FALSE OP_IF …
+OP_ENDIF` wrapping any number of data pushes. Because envelopes are effectively
+no-ops, they do not change the semantics of the script in which they are
+included, and can be combined with any other locking script.
+
+A text inscription containing the string "Hello, world!" is serialized as
+follows:
+
+```
+OP_FALSE
+OP_IF
+  OP_PUSH "ord"
+  OP_1
+  OP_PUSH "text/plain;charset=utf-8"
+  OP_0
+  OP_PUSH "Hello, world!"
+OP_ENDIF
+```
+
+First the string `ord` is pushed, to disambiguate inscriptions from other uses
+of envelopes.
+
+`OP_1` indicates that the next push contains the content type, and `OP_0`
+indicates that subsequent data pushes contain the content itself. Multiple data
+pushes must be used for large inscriptions, as one of taproot's few
+restrictions is that individual data pushes may not be larger than 520 bytes.
+
+The inscription content is contained within the input of a reveal transaction,
+and the inscription is made on the first sat of its first output. This sat can
+then be tracked using the familiar rules of ordinal theory, allowing it to be
+transferred, bought, sold, lost to fees, and recovered.

docs/src/introduction.md

@@ -26,6 +26,8 @@ fringe ordinal theorists.
 
 For more details on ordinal theory, see the [overview](overview.md).
 
+For more details on inscriptions, see [inscriptions](inscriptions.md).
+
 When you're ready to get your hands dirty, a good place to start is with
 [inscriptions](guides/inscriptions.md), a curious species of digital artifact
 enabled by ordinal theory.