diff --git a/reference/var/functions/is-numeric.xml b/reference/var/functions/is-numeric.xml
index 47967937a5..e6d5a76512 100644
--- a/reference/var/functions/is-numeric.xml
+++ b/reference/var/functions/is-numeric.xml
@@ -16,6 +16,7 @@
   </methodsynopsis>
   <para>
    Finds whether the given variable is numeric. Numeric strings consist of optional
+   whitespace, optional
    sign, any number of digits, optional decimal part and optional exponential part.
    Thus <literal>+0123.45e6</literal> is a valid numeric value. Hexadecimal (e.g.
    <literal>0xf4c3b00c</literal>) and binary (e.g. <literal>0b10100111001</literal>)