Constant VDOM_CALLS 

pub const VDOM_CALLS: &'static [&'static str];

Every vdom.lg function a lowered page calls — the tape it writes, the commit, the sites and fragments it finds its nodes by. None of them appears in the author’s source, so the prelude splices vdom.lg for a page and the pruner keeps exactly these as roots (loader.rs); vdom_calls_lock holds this list to the calls the lowering writes.