You may also find useful knowing that you can also validate the type of files attached.
Let's suppose we want to validate that our issue has the following files attached:
At least 1 .jar file.
At least 3 images (any format).
No more than 5 .txt file
Exactly 1 XML file.
To implement this validation we will use Boolean validator with math, date-time or text-string terms with the following configuration:
Boolean expression used is: matches(%{00072}, "(.*application/java-archive.*){1,}") AND matches(%{00072}, "(.*text/plain.*){0,5}") AND matches(%{00072}, "(.*text/xml.*){1}") AND matches(%{00072}, "(.*image/.*){3,}")
Note that:
To design this configuration, I have previously used Copy a parsed text to a field post-function in order to see the value that field "Attachments with details" takes when I attach different file types. Then it's easy to write a regular expressions for matching desired values.