You provide either search bounds or an initial guess; this section explains how search bounds and guesses work and how function arguments control them.
A guess is simply an @math{x} value which is iterated until it is within
the desired precision of a root. It takes the form of a double.
Search bounds are the endpoints of a interval which is iterated until the length of the interval is smaller than the requested precision. The interval is defined by two values, the lower limit and the upper limit. Whether the endpoints are intended to be included in the interval or not depends on the context in which the interval is used.