Big @formulas are easier to write in JEdit, here is my editing mode.

Put it in the modes directory of JEdit, add the following lines to the catalog file in the same directory (it has to go between the MODES-tags):

<MODE NAME="atformula" FILE="atformula.xml" FILE_NAME_GLOB="*.{atformula,at}" />

When you open a file with the extension .at or .atformula, JEdit will do syntax highlighting.

Keep in mind that this is the first version, and there might be ”bugs” in it. If you find any, please let me know!