diff --git a/zip-0315.rst b/zip-0315.rst
index 4a6cf5e1..1bf68fee 100644
--- a/zip-0315.rst
+++ b/zip-0315.rst
@@ -38,6 +38,12 @@ Transaction output (TXO)
     An output (transparent coin or shielded note) of a transaction on the consensus
     block chain or in the mempool visible to a wallet.
 
+TODO: Add informal definitions of:
+* known-spendable and confirmed-spendable TXOs;
+* trusted and untrusted TXOs.
+
+These should forward-reference the specification section with the formal definitions.
+
 
 Motivation
 ==========
@@ -88,24 +94,29 @@ share some of their keys.
 Prompt accessibility of funds
 -----------------------------
 
-Wallets need to take account of two concerns:
+Wallets need to take account of two main concerns with respect to
+accessibility of funds:
 
 * enabling funds to be spent as quickly as possible to reduce latency;
-* waiting long enough before spending TXOs to ensure that the
-  confirmed-spendable balance is not overestimated, and so can be trusted
-  by the user.
+* ensuring that the confirmed-spendable balance is not overestimated,
+  and so can be trusted by the user.
+
+These concerns affect the way that balances should be computed, which
+notes are selected for spending, and how the wallet should ensure that
+sufficient notes are available to cover multiple spends within a short
+period.
 
 To support this we define two kinds of TXOs:
 
-* A trusted TXO is a TXO received from a party where the wallet trusts a
-  double-spend not to occur, e.g. TXOs created by the wallet's internal TXO
-  handling.
+* A trusted TXO is a TXO received from a party where the wallet trusts that
+  it will remain mined in its original transaction, such as TXOs created by
+  the wallet's internal TXO handling.
 * An untrusted TXO is a TXO received by the wallet that is not trusted.
 
-
 Wallets can then require that untrusted TXOs need more confirmations before
-they become spendable than trusted TXOs. This provides an improved trade-off
-between latency on the one hand, and reliability and safety on the other.
+they become confirmed-spendable than trusted TXOs. This provides an improved
+trade-off between latency on the one hand, and reliability and safety on the
+other.
 
 
 Specification