The interval in which the function \( f(x) = x^x, \ x > 0 \), is strictly increasing is:
\( \left[\dfrac{1}{e}, \infty\right) \)
\( (0, \infty) \)
\( \left(0, \dfrac{1}{e}\right] \)
\( \left[\dfrac{1}{e^2}, 1\right] \)