Final answer:
The question seems to mention HTML custom tags incorrectly as and . Custom tags in HTML5 should have a hyphen in their names, such as , and must have defined behavior with JavaScript and CSS.
Step-by-step explanation:
It seems there might be a bit of confusion in your question. If you are referring to HTML custom tags, the idea is that developers can create their own tags in HTML5 with unique behavior defined by them using JavaScript and CSS. Typically, such custom tags need a hyphen in their names to be valid, e.g., <my-custom-tag>. However, if <and> and <custom> were to be presumed as custom tags, they wouldn't be proper since they lack the hyphen and are not standard tags in HTML5.