".c" files always contain "lite-c" code. ".wdl" files always contain "c-script" code or world definition language as it was called in ancient times. These are two different (yet very similiar) programming languages. SED won't care if you use lite-c or c-script. However, if you have a .c file it will always be interpreted as lite-c and .wdl files always as c-script. If you're new to programming i recommend choosing either lite-c or c-script and starting to learn it. My personal selection would be lite-c. It's more flexible and will be the future of 3dgs. If you're able to programm in lite-c you'll understand any c-sript code anyways.

You can include .wdl files in .c files but not vice versa and my personal recommandation is to never mix the two.