A footnote is a reference of an explanatory note at the bottom of the page. They are usually small numbers alongside a word or sentence.
note reference marks
Note Reference Marks
In MLA style, the superscript number is used as a note reference mark to signal the existence of an explanatory note. The superscript number corresponds to the note located at the bottom of the page or end of the document.
a superscript
footnote
it is a header
Shut up and get a life
flag
A Boolean variable can be used to signal when a condition exists. It can have a value of true or false based on whether the condition is met or not.
By definition a continuous signal is just that continuous to have no amplitude is to mean it doesn't exists
display only when immediate or potential danger exists
Display only when immediate or potential danger exists