f7723559_CSS_HTML_XHTML_Reference_Book__Description_and_notes
[Property/Values] margin one to four of the following: length, percentage, or auto, or inherit [Description and notes] 
for setting the amount of space between one or more sides of an element's border and its parent element initial value depends on browser and on value of width; not inherited; percentages refer to width of containing block
CSS HTML XHTML Reference Book
Description and notes