PEAR_Size has a number of output drivers which provide a means of providing reports in a range of various formats in an extensible manner - they all extend the PEAR_Size_Output_Driver class.
Four drivers are currently available for use:
CSV, PEAR_Size_Output_CSV. Print a comma separate values of results.
HTML, PEAR_Size_Output_Html. Print reports in HTML.
Text, PEAR_Size_Output_Text. Prints the reports in pure text - no additional formatting.
XML, PEAR_Size_Output_XML. Prints the reports in XML.
If these drivers are not adequate for what you require, you should consider writing your own - based on the PEAR_Size_Output_Driver class.