backtrack method
Implementation
@pragma('vm:prefer-inline')
@pragma('dart2js:tryInline')
void backtrack(int pos) {
  if (isRecoverable) {
    this.pos = pos;
  }
}@pragma('vm:prefer-inline')
@pragma('dart2js:tryInline')
void backtrack(int pos) {
  if (isRecoverable) {
    this.pos = pos;
  }
}