Constant MAX_LOAD_BYTES 

pub const MAX_LOAD_BYTES: usize = _; // 4_194_304usize

The most expanded macro text, counting what was expanded as well as what it came to, that a whole load should do, for Macros::with_budget to be given. Each expansion takes the size of its text and result, so this also bounds the lookups, and so the time, of a load.