Comment by conartist6

I'm talking about a universal placeholder, something that you're free to use anywhere, in any language, for any part of a syntax tree that is missing.

A TODO comment can't do that because the syntax conflicts. For a regex the conflict would look like `//* TODO *//`, and for a comment it would look like `// /* TODO */`. Both have an existing meaning, and in neither case is that the meaning I want.

If I could have a magic "stuff goes here" character this would be solved. I often use · to represent the idea of this magic character. That gives you /·/ and //· at least, but of course it isn't safe to assume that no language will ever assign meaning to the · character so we can't literally use it as the universal gap. To get something universal, you need to move from using a sentinel token to using embedded/encoded data.