The <frameset> tag is used to proportion the frames within the browser. The 'cols' attribute divides the page vertically into two or more columns. Alternatively, you can use the 'rows' attribute to create horizontal divisions in the document.

The argument to either the 'rows' or 'cols' attribute specifies the size of each frame. This size can be expressed as a percentage of the browser window by appending a percentage symbol (%) to the number.

The argument can also specify an absolute size by including a number representing the size of the frame in pixels:

<frameset rows = "*, 120">

Finally, the asterisk is used to represent the remaining screen space.