devs/outputmessages.md

+# Output user messages
+
+In this section you will find how to properly output information, warning or error messages for the end user.
+
+## Diagnostics Class
+You can use a special class designed to output warning or fatal error messages to the user.
+The code is in the following package and class:
+
+```java
+package ltsa.lts;
+
+public class Diagnostics {...}
+
+```
+
+In order to use Diagnostics, you must first initialize the default output option. 
+
+In case you are using the UI, you need to initialize it with the LTSOuput used by the main window.
+
+```java
+Diagnostics.init(out);
+```
+
+From _MTSA> Options> Treat Warnings as errors_ you can force warnings to raise an exception.
+
+
+### Warning and Fatal
+Fatal errors can be used just with a string message or marking the symbol or position of the error.
+
+Warning messages can be used just with the string message.
+
+
+## log
+In some places it is also use the java logger. It is not recommended for end user, only for techinical log output.
+
+```java
+import org.apache.log4j.Logger;
+
+private Logger logger = Logger.getLogger(this.getClass().getName());
+logger.error("Scheduler factory not found");
+```
+
+## System.out.println()
+This practice is discourage. Use only for testing and debugging purposes.
+
+---