In a browser, this page looks very different than in the HTML source code. Observe all of the whitespace in the HTML source code around these sentences. Whitespace includes consecutive spaces, tabs, line returns, and blank lines. A web browser removes all whitespace EXCEPT single blank spaces. Single spaces must be preserved so that consecutive words have a space in between.

In a browser, the indentation at the beginning of this sentence is gone. The consecutive spaces in this sentence are gone. All the blank lines between these sentences are gone. ALL formatting requires HTML markup elements like the two line breaks that separate the two paragraphs you see in a browser.