This is a simple taglib for Marko.js (github.com/marko-js/marko) which adds <let> and <const> tags, using functionality which was already built into the compiler but never exposed through built-in tags.
The reason for this being a separate package is to allow developers to experiment with these tags without breaking compatibility, as discussed in marko-js/marko#428. If and when these tags are added the Marko compiler or an official taglib, this package is to be considered deprecated.
The <let> and <const> tags are functionally identical to the built-in <var> tag (as of Marko v3.12.0) except that they generate the let and const keywords rather than var in the compiled output.