There are some generally understood guidelines but there is really no canonical documentation about formatting like in stackoverflow.
The Spanish SE community is still too small to see a prevalent pattern of formatting in answers or questions.
Eventually though we will have to have some guidelines for this.
Some of the things I have seen so far as "tacit" rules are:
Definitions from the rae are quotes
Hello I am a RAE definition
Words that need emphasis can be bold or in italic.
This is an important word.
Incorrect words can be bold or in italicstriken-through.
This is an
And that is all that comes to mind right now. I will complete this answer if something else comes up though.