This is a pair of functions to manipulate the hold state of an axes object.

The first one holds the axes for adding multiple new graphics objects. It can optionally clear them first, if the previous hold state was off.

This is useful when a function either:

1) adds graphics without erasing anything, ignoring the existing hold state, or

2) behaves like plot, but needs to temporarily add multiple objects to the plot.

The second function restores the axes object to its previous hold state.