Macro parse_block 

macro_rules! parse_block {
    ($input:ident, $comments:expr, {
        $($($key:literal)|+ => $target:ident : $parser:expr $(=> $action:block)? ),* $(,)?
    }, $break_condition:expr $(, $error_label:expr)?) => { ... };
    (@action $comments:expr, $loop_comments:ident, $val:ident, $target:ident) => { ... };
    (@action $comments:expr, $loop_comments:ident, $val:ident, $binding:ident, $action:block) => { ... };
}

Macro for declarative KVN block parsing.

This macro generates a loop that matches keys using dispatch!, handles comment collection, and provides helpful context on errors.