tl:dr; Use //*/ to terminate block comments, then use /* and //* to toggle the block in and out of code.

So this is a small trick but it’s really useful — a syntax hack at the same kind of level of a keyboard shortcut.

Most C-syntax langauges use line comments and block comments like so;

// line comment

/*
block comment
*/

Block comments mask more code, but they tend to be ‘fiddly’ to put into your code and take out. This can be a pain when you have a block you’re developing and you want to comment it in and out regularly;

/*
... big code block here
... which goes on for a while
... and you want to toggle it
... in and out regularly.
*/

So if you change your terminating symbol to //*/, an interesting thing happens; it functions as the terminator of a block comment inside a block comment, but a line comment otherwise. This means you can toggle code in and out by putting a single extra slash on the start of the block comment;

/*
code here commented out
//*/

but

//*
code here is now active
//*/

So there is it. A single-character togle of a block comment.