For checking a regular expression in input fields of HTML forms which attribute

For checking a regular expression in input fields of HTML forms which attribute is used?

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1) Which of the following element represents the header of a section or the document and contains a label or other heading information for the related content?

2) Which of the following attribute adds audio controls, like play, pause, and volume?

3) In HTML5 how many new semantic elements were introduced?

4) Which of the following element sets is an item of microdata?

5) Which element represents a control for generating a public-private key pair?