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(?<=\[(\w\w)-I\])[^\]]+(?=\[\1-F\])

It's hard to determine exactly what your rules are, so I used these:

The opening tag is defined as a left square-bracket followed by 2 word
characters, followed by a hyphen, followed by the character 'I', followed by
a right square-bracket. The closing tag is defined as a left square-bracket,
followed by the same 2 word characters in the opening tag, followed by a
hyphen, followed by the character 'F'. I used a positive look-behind, with a
group around the 2 characters preceding the hyphen, assumed that the
contents between would not contain the left squaare-bracket, and would
consist of at least one character, and a positive look-ahead, referencing
the same group from the positive look-behind. This results in a set of
matches of all characters between the opening and closing tags as I defined
them.