If the tag is left open, how will browsers perceive and process it?

Question

SVG

Good afternoon!
Actually, the question is already

Answer 1

See what the tag is.
In some (many) cases, the browser may correctly process a block with an unclosed tag.
IDE prompts where left unclosed.
But, of course, it is better to always close. As far as I know, HTML5 forbids unclosed tags.
And so - the design will "go", bugs with markup and incorrect behavior of scripts will climb.