%bb replicates the syntax of %bt (Button) but has certain advantages.
1. %bt (Button) does not always respond to the application of an XP theme when a manifest is used (or when this is the default) so it can appear to be out-dated. For example, this is the case when an icon is used with %bt (Button) or the background colour is changed from the default.
2. %bb is simpler to use when an icon is added and, unlike %bt, icons are not limited to the size 32x32.
The only limitation of %bb when compared with %bt (Button) is that it will not accept multi-line text.
%bb[MY_ICON/Button text] provides a button that displays the icon resource MY_ICON followed by the text "Button text". %bb[MY_ICON//Button text] is the same but the icon will not be greyed when the button is disabled.
Like %bt (Button), %bb can be used with %bi (Button Icon), %bc (Button Background Colour), %bu (Button Text Colour), %`bc, and %`bu. It can also take an accelerator key on a character prefixed by an ampersand and can take an integer (e.g. %6bb[OK]) in order to set the width of the text. You can use %bb with or without an icon or with an empty text part.