Messages are the bones of the Livecode programming language. First of all let's see the path of the events:
A message is a function that reacts on a event with its name. When an event like "MuoseUp" passes through a button with that message, it activates that message. The event can stop there or be passed to the next object. To pass to the next object in hierarchy use pass keyword:
A message it's like function of other programming languages. A message starts with "on MessageName" and ends with "end MessageName", like this:
on MyMessage answer "Hello world" end MyMessage
Messages can have optional values (parameters), look the following example:
on MyMessage myoption1, myoption2 answer "Hello world" & myoption1 & myoption2 end MyMessage
you can call it with all the following methods:
myMessage MyMessage 34 MyMessage 34,"hi"
Parameters not used are automatically set to empty.
You can't nest messages inside messages.
You can activate the message of another object in two ways: sending or calling it.
Sending a message, send the specified message to that object, and momentary that object reacts as it is the current active object:
send MouseUp to button MySpecialButton
Call put the message in the current object, so it's behaviour may change:
call "MyMessage 34,hi" of button "myButton"
notice the use of double quote to insert parameters