How can I can insert the contents of a file into another file right before a specific line

Question

How can I can insert the contents of a file into another file right before a specific line using sed?

example I have file1.xml that has the following:

Answer 1

Usually I do like this:

1. file1, file to read insert content
2. file2, insert reading content from file1 to at the head of file2

3. script snippet:

   sed "\$r ${file2}" ${file1} > tmpfile
mv tmpfile ${file2}