ที่มา: http://www.devx.com/tips/Tip/13638
It’s fairly easy to confuse the Cascading Style Sheets (CSS) properties display and visibility, because it would seem that they do much the same thing. However, the two properties are in fact quite different. The visibility property determines whether a given element is visible or not (visibility=”visible|hidden”). However, when visibility is set to hidden, the element being hidden still occupies its same place in the layout of the page.