Question

which behaviour of a tag can be controlled using the opening tag
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Answer 1

HTML attributes are special words used inside the opening tag to control the element's behaviour. HTML attributes are a modifier of an HTML element type. An attribute either modifies the default functionality of an element type or provides functionality to certain element types unable to function correctly without them. In HTML syntax, an attribute is added to an HTML start tag.

Answer 2

HTML Marquee Tag

hope it helps !!