Specifies the nature of the content sizing if the size_panel_to_content is not false().
Use this property with care. Although the panel does its best to do what you expect, some decisions about content size and placement of scroll bars are determined by the browser using its own rules. This may lead to unexpected behaviour. In particular, layouts that use percentages to size elements may result in unexpected scroll bars.
'both' – the height and width of the panel are resized.
Set to 'height' to size the panel's height only. Set to 'width' to size the panel's width only. Set to 'both' to size the panel's height and width.