Is there a way to include an expand text button in your article? Making a more streamlined essay, but allowing the reader to click the button for an expanded definition or for background information. Many forums will have a "spoiler" button to hide text unless clicked by the reader.

It looks like you're in the Fancypants mode of editing, which will convert all formatting characters into plain text characters. You can either switch to WYSIWYG mode or you can select the text you want to hide, making sure you do not have any spaces on either side, and use the spoiler formatting button.

Type > ! before your spoiler, then then type ! < afterwards. Do not use spaces in the codes or between the codes and the first and last characters of your spoiler. I put spaces in for illustrative purposes only.

I have seen spoilers on forums (including my own) that are not just text with the background color changed. They have the content hidden until you click a show/hide toggle button. I want to add a section to a site that doesn't show up by default to save space.

I want this feature because I post supplementary materials (code) in my questions on math.stackoverflow, which is useful to maybe 5% of the people who read my question, so I want to use something like "spoiler" to hide it by default. Edit: Blogger calls it "expandable summary" and LiveJournal calls it "cut" and uses tag "lj-cut".