# DP: Clarify documentation about substring expansion

--- a/bash/doc/bash.1
+++ b/bash/doc/bash.1
@@ -2758,6 +2758,9 @@
 below).
 If \fIoffset\fP evaluates to a number less than zero, the value
 is used as an offset from the end of the value of \fIparameter\fP.
+Arithmetic expressions starting with a - must be separated by whitespace
+from the preceding : to be
+distinguished from the \fBUse Default Values\fP expansion.
 If \fIlength\fP evaluates to a number less than zero, and \fIparameter\fP
 is not \fB@\fP and not an indexed or associative array, it is interpreted
 as an offset from the end of the value of \fIparameter\fP rather than