Running and controlling TeX

! Usually, all you will ever need is a single `texrunner` instance which
controls a single running TeX or LaTeX instance at a time. To make life easy to
our users..., such an instance is created automatically upon startup and its
called the `defaulttexrunner`. Whenever you use the function shortcuts like
`text.text()` and in particular `text.set()`, you are accessing this
`defaulttexrunner` instance. Also, the shortcut method `text` of any canvas
instance uses this `defaulttexrunner` by default.

!! However, it is possible to create several texrunner instances. In this
example, we are using two of them. To make it a little more interesting, we
instruct the `defaulttexrunner` to use LaTeX, while keeping TeX for the
`plaintexrunner` instance. It is you turn to try expressions valid in TeX or
LaTeX only at the different `texrunner` instances.

!! Note that you do not have to worry about mixing the results of different
texrunners into a single output. Even the embedded fonts in the output are
shared. You can, by the way, also restart a `texrunner` instance including the
`defaulttexrunner` and change its configuration on that occasion.
