    curve.tAt(ratio [, opt])

Return the `t` value of the point that lies `ratio` (normalized length) away from the beginning of the curve.

The function expects `ratio` to lie between 0 and 1; values outside the range are constrained to 0 and 1, respectively.

The function uses the same algorithm as the `curve.tAtLength()` function.

The default value for `opt.precision` is 3; this corresponds to maximum observed error of 0.1%.

The `opt.subdivisions` property may be specified, directly providing an array of pre-computed curve subdivisions from which to calculate curve length. Use the `curve.getSubdivisions()` function to obtain an array of curve subdivisions. The `opt.precision` property is still necessary, however; it determines the precision of the point search algorithm.