uniform heading commands work in any context, even in theory header;
discontinued obsolete 'sect', 'subsect', 'subsubsect';
marked obsolete 'header' as legacy;
src/Pure
src/FOL
src/HOL
src/ZF
src/CCL
src/CTT
src/Cube
src/FOLP
src/LCF
src/Sequents
src/Doc
src/Tools