Deriving conserved currents by promoting parameter

Question

I currently reading Tong's text on String Theory.

In Chapter 4.1.1 he alludes to a technique to derive conserved currents

Recall that we can usually derive conserved currents by promoting the constant parameter $\epsilon$ that appears in the symmetry to a function of the spacetime coordinates.

Since I don't know what he refers to, could someone provide me a proper reference?

Answer 1

Tong is alluding to the standard trick in the derivation of Noether's theorem by promoting the (infinitesimal) $x$-independent parameter $\epsilon$ to become $x$-dependent, see e.g. this Phys.SE post.