It's old-school plain-text email etiquette. The original Markdown even used a variant of that syntax for its links definition, known as "reference links". https

It's old-school plain-text email etiquette. The original Markdown even used a variant of that syntax for its links definition, known as "reference links". https://daringfireball.net/projects/markdown/syntax#link https://daringfireball.net/projects/markdown/syntax#link