diff --git a/doc/pcre2grep.1 b/doc/pcre2grep.1
index 513a15f..75e5685 100644
--- a/doc/pcre2grep.1
+++ b/doc/pcre2grep.1
@@ -1,4 +1,4 @@
-.TH PCRE2GREP 1 "01 April 2016" "PCRE2 10.22"
+.TH PCRE2GREP 1 "06 April 2016" "PCRE2 10.22"
 .SH NAME
 pcre2grep - a grep with Perl-compatible regular expressions.
 .SH SYNOPSIS
@@ -675,7 +675,7 @@ following substrings specifying arguments:
 .sp
   executable_name|arg1|arg2|...
 .sp
-Any substirng (including the executable name) may contain escape sequences
+Any substring (including the executable name) may contain escape sequences
 started by a dollar character: $<digits> or ${<digits>} is replaced by the
 captured substring of the given decimal number, which must be greater than
 zero. If the number is greater than the number of capturing substrings, or if
@@ -695,10 +695,14 @@ a single dollar and $| is replaced by a pipe character. Here is an example:
     Arg1: [1] [234] [4] Arg2: |1| ()
     12345
 .sp
-Any syntax errors in the string (for example, a dollar not followed by another 
-character) cause the callout to be ignored. If running the program fails for 
-any reason (including the non-existence of the executable), a local matching 
-failure occurs and the matcher backtracks in the normal way.
+The parameters for the \fBexecv()\fP system call that is used to run the
+program or script are zero-terminated strings. This means that binary zero
+characters in the callout argument will cause premature termination of their
+substrings, and therefore should not be present. Any syntax errors in the
+string (for example, a dollar not followed by another character) cause the
+callout to be ignored. If running the program fails for any reason (including
+the non-existence of the executable), a local matching failure occurs and the
+matcher backtracks in the normal way.
 .
 .
 .SH "MATCHING ERRORS"
@@ -748,6 +752,6 @@ Cambridge, England.
 .rs
 .sp
 .nf
-Last updated: 01 April 2016
+Last updated: 06 April 2016
 Copyright (c) 1997-2016 University of Cambridge.
 .fi