From dcd17c203cbcde19ff026fc05bba7e79350165eb Mon Sep 17 00:00:00 2001
From: P. J. McDermott <pjm@nac.net>
Date: Wed, 24 Oct 2012 18:25:21 -0400
Subject: Document substitution variables.

---
(limited to 'specs/spf-2.0/substvars.mdwn')

diff --git a/specs/spf-2.0/substvars.mdwn b/specs/spf-2.0/substvars.mdwn
new file mode 100644
index 0000000..bbe2853
--- /dev/null
+++ b/specs/spf-2.0/substvars.mdwn
@@ -0,0 +1,19 @@
+Variable Names [substvars-name]
+===============================
+
+Variable names may only consist of uppercase and lowercase Latin letters,
+digits, and hyphens.  Names must be at least one character long.  (A regular
+expression for this is `[A-Za-z0-9-]+`.)
+
+
+Variable Substitutions [substvars-exp]
+======================================
+
+Variable substitutions are performed on certain binary control field values, as
+explained in $[sectlink][fields-bin].
+
+The format for variable substitutions is as follows:
+
+    ${<var-name>}
+
+`<var-name>` is the name of the variable.
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