Doc: Usage: Added a clarifying paragraph about Error Messages

Issue 3873

Added a clarifying paragraph explaining that (the same)
diagnostics message can occur in multiple places for
(the same) input depending on the type and its context.

diff --git a/Documentation/usage/running.itely b/Documentation/usage/running.itely
index 95bbafd10383153aeb5083b6ff2c7c3c5a249145..0bff8f68df9636786d7eed1e0fdf43b83b8e4ea2 100644 (file)
--- a/Documentation/usage/running.itely
+++ b/Documentation/usage/running.itely
@@ -915,6 +915,13 @@ when something unexpected happens.  If you can't see an error in the
 indicated line of your input file, try checking one or two lines
 above the indicated position.
 
+Please note that diagnostics can be triggered at any point during the
+many stages of processing.  For example if there are parts of the input
+that are processed multiple times (i.e. in midi and layout output), or
+if the same music variable is used in multiple contexts the same message
+may appear several times.  Diagnostics produced at a @q{late} stage (i.e
+bar checks) might also be issued multiple times.
+
 More information about errors is given in @ref{Common errors}.