Compare by content ignores case difference.

[DimitriAus]

Steps to repeat: Change case of a latter in a text file. Compare to original file. No changes shown.
Expected: line with the changed latter highlighted.

[MVV]

Have you checked "Case sensitive" option?

[ManlyElectronics]

No, my fault for not knowing, but.. It is a matter of common sense a convenience. I expected to compare 100% with the default settings.
'Case sensitive' is a Filter omitting something, same with spaces and lines.