I am working with one graph algorithm and there is a term in it that I do not understand. It is the size of a graph vertex. Moreover, in such a context that the size of a graph can also be determined using the sizes of the graph vertices.

Text from algorithm:

The algorithm works by traversing the nesting tree T in depth. At each
step, a fragment is laid out using the sizes and locations of the
vertices or other fragments directly embedded in it. Note that after
constructing the image of a fragment, its sizes can be calculated and
used when laying out the fragment in which the fragment is directly
embedded.

Please help me how to find the size of a graph vertex and how to use these sizes to calculate the size of the graph in which these vertices are located.