By default, text at the start of a line (or after only white space) represents an html tag. Indented tags are nested, creating the tree like structure of html.

Pug also knows which elements are self closing:

Block Expansion

To save space, Pug provides an inline syntax for nested tags.

Self Closing Tags

Tags such as img, meta, and link are automatically self-closing (unless you use the XML doctype). You can also explicitly self close a tag by simply appending the / character. Only do this if you know what you’re doing.