1vw = 1% of viewport height

The most common way to discover the type of a file, is to look at the file extension

Multimedia files have formats and different extensions like: .wav, .mp3, .mp4, .mpg, .wmv, and .avi

Only MP4, WebM, and Ogg audio are supported by the HTML standard

Only MP3, WAV, and Ogg video are supported by the HTML standard

The controls attribute adds video controls, like play, pause, and volume

The <source> element allows you to specify alternative video files which the browser may choose from. The browser will use the first recognized format.

The text between the <video> and </video> tags will always be displayed

Add muted after autoplay to let your video start playing automatically (but muted)

To play an audio file in HTML, use the element <video>

Add mute=1 after autoplay=1 to let your video start playing automatically (but muted)

XHTML stands for EXtensible HyperText Markup Language

html is stricter than XHTML

XHTML is more XML-based version of HTML

XHTML is HTML defined as an XML application

XHTML isn’t supported by all major browsers

XHTML was developed to make HTML more extensible and flexible to work with other data formats (such as XML)

browsers don’t ignore errors in HTML pages

XML is a markup language where all documents must be marked up correctly (be "well-formed")

XHTML comes with a much stricter error handling

in XHTML <!DOCTYPE>