The button has the following possible attributes:

action	action = "(function)";	Specifies an AutoLISP expression to perform an action when this tile is selected.
alignment		For a tile that is a child of a column, the possible values are left, right, or centered (default is left). For a tile that is a child of a row, the possible values are top, bottom, or centered (default is centered).
is_cancel	true or false	Selecting the button causes the dialog to be terminated if the button's action does not call done_dialog.
is_default	true or false	Specifies whether the button is the default button selected (“pushed”) when the user presses the accept key.
is_enabled	true or false	determines if tile is accessible to user
is_tab_stop	true or false	Specifies whether the tile receives keyboard focus when the user moves between tiles by pressing the Tab key.
key	unique string	the name the program uses to refer to this tile
label	string	The text to be displayed in the tile. If a character is preceded by an ampersand, that character is the mnemonic.
mnemonic	single character	Focus goes to this tile when the character is pressed.
fixed_height
fixed_width
height
width	integer	width in unknown units

Sample:

    : button {
        label = "Ductwork";
        key = "1";
        value = "ductwork";
    }