The signature is used to filter files in addition to the files extensions. This panel is used to enter that signature into ECMerge. Many file formats have a recognizable start with a few bytes set to particular values (e.g. MS Windows executables all start with 'MZ' letters).
First/Last offset to test
Attempts to recognize the signature will happen at each offset in the file between first and last offsets included, until the signature is found.
Signature / Mask
each character code is used to code on bytes of the signature
(use \xhh to code non-printable values).
When the mask is not set, it is the equivalent of having a
string made of \xFF as long as the signature.
A helper button placed to the right of the signature and mask fields helps you to enter scripting escape sequences.