[jlesk]

Double-arrows let you signify that the tag is different with no extra effort because it's just an extra tap where your finger is already positioned.

It also has a right directionality to imply that it has scope until the end of the line.

Triple-arrow is the same idea, but uses the convention that triple-characters are common for delineating multi-line blocks.

[jetti]

I get that it is convenient but it just seems like the syntax is prone to unexpected behavior from typos.