array which forms a stack to keep track of nested callback functions
the objectId (number within the objects array) of the document catalog
store the stack for the transaction commands, each item in here is a record of the values of all the variables within the class, so that the user can rollback at will (from each 'start' command) note that this includes the objects array, so these can be large.
current colour for fill operations, defaults to inactive value, all three components should be between 0 and 1 inclusive when active
object number of the currently active contents block
a record of the current font
the number of the current font within the font array
current style that lines are drawn in
object number of the current page
current colour for stroke operations (lines etc.)
track if the current font is bolded or italicised
should be used for internal checks, not implemented as yet
draw a bezier curve based on 4 control points