Question: When adding non-critical extensions to a message that has been critically extended, what should be avoided when possible?
Option 1: Including critical extensions in earlier branches of the message
Option 2: Including non-critical extensions in earlier critical branches of the message
Option 3: Using extension markers for all types of extensions
Option 4: Placing extensions at the highest level in the message
Explanation: According to the guidelines, when further non-critical extensions are added to a message that has been critically extended, the inclusion of these non-critical extensions in earlier critical branches of the message should be avoided when possible. This is to prevent unnecessary complexity and potential conflicts between critical and non-critical extensions.