code: function(ratio, opt) {
  
              if (ratio <= 0) return 0;
              if (ratio >= 1) return 1;
  
              opt = opt || {};
              var precision = (opt.precision === undefined) ? this.PRECISION : opt.precision;
              var subdivisions = (opt.subdivisions === undefined) ? this.getSubdivisions({ precision: precision }) : opt.subdivisions;
              var localOpt = { precision: precision, subdivisions: subdivisions };
  
              var curveLength = this.length(localOpt);
              var length = curveLength * ratio;
  
              return this.tAtLength(length, localOpt);
          }
docs: Returns `t` at requested `ratio` with precision better than requested `opt.precision`; optionally using `opt.subdivisions` provided.