Shell programming and Kate

A question about shell programming and the Kate editor (or KWrite). When using Kate (or KWrite) for shell programming I normally do not get sytnax high-lighting. I assume this is because most scripts do not have a file extension. If I add the file extension "sh" then I get syntax high-lighting. Two questions.. - Why are file extensions rarely used on shell scripts? - If I start using a file extension (like "sh") what would be the most appropriate extension for bash scripts? And a third questions... - What is the best editor (your opinion) in the Suse distro (I'm using 8.1) for shell programming? For PHP programming? Thanks! Matt