Mark is a formatting element used to high light text in document. You can use mark tag to high light text as important to viewer
<mark>Content</mark>
Or
<tag><mark>Content</mark></tag>
You can apply mark element to any element and use any where within a HTML document.
Mark is a pair tag and output of mark element is high lighted text like you can see in above example.
Open notepad or any other text editor, follow the following points.
save file with name task.html or task.htm and then open it using any browser and see results.
Don't forget mark is non empty element which means it always comes in pair.