The documentation is not very clear on this.
name - String - Button name to add.
settings - Object - Settings object with title, cmd etc
autofocus
: True if the control should be focused when renderedborder
: Border box values example: 1 1 1 1classes
: Space separated list of classes to adddisabled
: Is the control disabled by defaulthidden
: Is the control hidden by defaulticon
: Icon to use for buttonimage
: Image to use for iconmargin
: Margin box values example: 1 1 1 1minHeight
: Minimal height for the controlminWidth
: Minimal width for the controlname
: Name of the control instancepadding
: Padding box values example: 1 1 1 1role
: WAI-ARIA role to use for controlsize
: Size of the button small|medium|largestyle
: Style CSS properties to addtext
: Text to display inside widgettooltip
: Tooltip text to display when hoveringFor a full list of all the settings and methods see the TinyMCE documentation page