The distinction is that stuff you "hide" in a readmore will show up if anyone looks at your node directly, where as the poster is suggesting a new tag which would never show up when viewing the node (either in a list, or directly) and would only be included as part of the "d/l code" content.

The advantage of readmore tag is being able to shorten the node if you just want an overview.

The advantage of a "hidden_code" tag would be that you could allways make "d/l code" provide a complete program, with all neccessary use statements and helper functions, but reading the node would only include the specific code you have a question about.