diff --git a/11-payment-encoding.md b/11-payment-encoding.md
index 0db670636..d22d4de8a 100644
--- a/11-payment-encoding.md
+++ b/11-payment-encoding.md
@@ -9,6 +9,7 @@ over Lightning.
   * [Human-Readable Part](#human-readable-part)
   * [Data Part](#data-part)
     * [Tagged Fields](#tagged-fields)
+    * [Feature Bits](#feature-bits)
   * [Payer / Payee Interactions](#payer--payee-interactions)
     * [Payer / Payee Requirements](#payer--payee-requirements)
   * [Implementation](#implementation)
@@ -140,6 +141,9 @@ Currently defined tagged fields are:
    * `fee_base_msat` (32 bits, big-endian)
    * `fee_proportional_millionths` (32 bits, big-endian)
    * `cltv_expiry_delta` (16 bits, big-endian)
+* `9` (5): `data_length` variable. One or more 5-bit values containing features
+  supported or required for receiving this payment.
+  See [Feature Bits](#feature-bits).
 
 ### Requirements
 
@@ -156,10 +160,13 @@ A writer:
       through some unspecified means.
         - SHOULD use a complete description of the purpose of the payment.
   - MAY include one `x` field.
+    - if `x` is included:
+      - SHOULD use the minimum `data_length` possible.
   - MAY include one `c` field.
     - MUST set `c` to the minimum `cltv_expiry` it will accept for the last
     HTLC in the route.
-  - SHOULD use the minimum `data_length` possible for `x` and `c` fields.
+    - if `c` is included:
+      - SHOULD use the minimum `data_length` possible.
   - MAY include one `n` field. (Otherwise performing signature recovery is required)
     - MUST set `n` to the public key used to create the `signature`.
   - MAY include one or more `f` fields.
@@ -175,6 +182,10 @@ A writer:
         `fee_base_msat`, `fee_proportional_millionths`, and `cltv_expiry_delta` are as
         specified in [BOLT #7](07-routing-gossip.md#the-channel_update-message).
     - MAY include more than one `r` field to provide multiple routing options.
+  - if `9` contains non-zero bits:
+    - SHOULD use the minimum `data_length` possible.
+  - otherwise:
+    - MUST omit the `9` field altogether.
   - MUST pad field data to a multiple of 5 bits, using 0s.
   - if a writer offers more than one of any field type, it:
     - MUST specify the most-preferred field first, followed by less-preferred fields, in order.
@@ -182,6 +193,11 @@ A writer:
 A reader:
   - MUST skip over unknown fields, OR an `f` field with unknown `version`, OR  `p`, `h`, or
   `n` fields that do NOT have `data_length`s of 52, 52, or 53, respectively.
+  - if the `9` field contains unknown _odd_ bits that are non-zero:
+    - MUST ignore the bit.
+  - if the `9` field contains unknown _even_ bits that are non-zero:
+    - MUST fail the payment.
+	- SHOULD indicate the unknown bit to the user.
   - MUST check that the SHA2 256-bit hash in the `h` field exactly matches the hashed
   description.
   - if a valid `n` field is provided:
@@ -253,6 +269,15 @@ engines that support SQL or other dynamically interpreted querying languages.
 
 Don't be like the school of [Little Bobby Tables](https://xkcd.com/327/).
 
+## Feature Bits
+
+Feature bits allow forward and backward compatibility, and follow the
+_it's ok to be odd_ rule.
+
+The field is big-endian.  The least-significant bit is numbered 0,
+which is _even_, and the next most significant bit is numbered 1,
+which is _odd_.
+
 # Payer / Payee Interactions
 
 These are generally defined by the rest of the Lightning BOLT series,
@@ -509,6 +534,44 @@ Breakdown:
   * `6c6e626332306d0b25fe64570d0e496dbd9f8b0d000dbb44824f751380da37c6dba89b14f6f92047d63f576e304021a00008101820283038404800081018202830384048000810182028303840480810243500c318a1e0a628b34025e8c9019ab6d09b64c2b3c66a693d0dc63194b02481931000` hex of data for signing (prefix + data after separator up to the start of the signature)
   * `399a8b167029fda8564fd2e99912236b0b8017e7d17e416ae17307812c92cf42` hex of SHA256 of the preimage
 
+> ### Please send $30 for coffee beans to the same peer, which supports features 1 and 9
+> lnbc25m1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5vdhkven9v5sxyetpdees9qzsze992adudgku8p05pstl6zh7av6rx2f297pv89gu5q93a0hf3g7lynl3xq56t23dpvah6u7y9qey9lccrdml3gaqwc6nxsl5ktzm464sq73t7cl
+
+Breakdown:
+
+* `lnbc`: prefix, Lightning on Bitcoin mainnet
+* `25m`: amount (25 milli-bitcoin)
+* `1`: Bech32 separator
+* `pvjluez`: timestamp (1496314658)
+* `p`: payment hash...
+* `d`: short description
+  * `q5`: `data_length` (`q` = 0, `5` = 20; 0 * 32 + 20 == 20)
+  * `vdhkven9v5sxyetpdees`: 'coffee beans'
+* `9`: features
+  * `qz`: `data_length` (`q` = 0, `z` = 2; 0 * 32 + 2 == 2)
+  * `sz`: b1000000010
+* `e992adudgku8p05pstl6zh7av6rx2f297pv89gu5q93a0hf3g7lynl3xq56t23dpvah6u7y9qey9lccrdml3gaqwc6nxsl5ktzm464sq`: signature
+* `73t7cl`: Bech32 checksum
+
+> # Same, but using invalid unknown feature 100
+> lnbc25m1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5vdhkven9v5sxyetpdees9q4pqqqqqqqqqqqqqqqqqqszk3ed62snp73037h4py4gry05eltlp0uezm2w9ajnerhmxzhzhsu40g9mgyx5v3ad4aqwkmvyftzk4k9zenz90mhjcy9hcevc7r3lx2sphzfxz7
+
+Breakdown:
+
+* `lnbc`: prefix, Lightning on Bitcoin mainnet
+* `25m`: amount (25 milli-bitcoin)
+* `1`: Bech32 separator
+* `pvjluez`: timestamp (1496314658)
+* `p`: payment hash...
+* `d`: short description
+  * `q5`: `data_length` (`q` = 0, `5` = 20; 0 * 32 + 20 == 20)
+  * `vdhkven9v5sxyetpdees`: 'coffee beans'
+* `9`: features
+  * `q4`: `data_length` (`q` = 0, `4` = 21; 0 * 32 + 21 == 21)
+  * `pqqqqqqqqqqqqqqqqqqsz`: b00001...(90 zeroes)...1000000010
+* `k3ed62snp73037h4py4gry05eltlp0uezm2w9ajnerhmxzhzhsu40g9mgyx5v3ad4aqwkmvyftzk4k9zenz90mhjcy9hcevc7r3lx2sp`: signature
+* `hzfxz7`: Bech32 checksum
+
 # Authors
 
 [ FIXME: ]