doc: note for awk macro fconv.

* txr.1: Add usage note to the fconv macro.

1 files changed, 11 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index 1829471c..8f9260d4 100644
--- a/txr.1
+++ b/txr.1
@@ -58388,6 +58388,17 @@ The return value of
 is
 .codn f .
 
+Note: because
+.code f
+is
+.code nil
+when no fields have been extracted, a
+.code fconv
+expression can be used as the condition in an
+.code awk
+clause which triggers the action if one or more fields have been
+extracted, and performs conversions on them.
+
 .TP* Examples:
 
 .verb