or keyboard 180 from the library on to the window i e model canvas the graphical version of the block that is rendered on the canvas is called the icon for the block there may be different embodiments for the library including a tree based browser view of all of the blocks an exemplary block library can be found in blocksets from the mathworks inc of natick mass including gauges blockset aerospace blockset signal processing blockset etc the users may define their own blocks using for example the s function provided in simulink u00ae in the illustrative embodiment the block diagram modeling environment 200 provides variant section blocks which will be described below in more detail with reference to fig4 6 users may build their block diagram models using the variant section blocks the illustrative embodiment provides four exemplary variant section blocks including a variant start block a variant end block a variant source block and a variant destination block one of ordinary skill in the art will appreciate that these four variant section block are illustrative and the present invention may be implemented using other alternatives such as those described below with reference to fig1 fig4 depicts an exemplary model 400 that includes a variant start block 410 and a variant end block 420 this pair of variant section blocks helps select various.