Brown's small graph principle for Feynman periods

Let $G$ be a primitive log-divergent Feynman graph, and let $[H_G,\omega_G,\sigma]^{\rm m}$ denote the motivic realisation of its Feynman integral $I_G^{\rm m}$. Let $\Delta$ denote the Galois coaction. Brown's small graph principle. The elements on the right-hand side of the coaction formula for $\Delta[H_G,\omega_G,\sigma]^{\rm m}$ can be expressed in the form

$$\prod_i[H_{\gamma_i},\omega_{\gamma_i},\sigma]^{\rm m},$$

where the product runs over a subset $\{\gamma_i\}$ of the set of subgraphs and quotient graphs of $G$.

The principle predicts that Galois conjugates of Feynman periods are built from periods associated with smaller subgraphs and quotient graphs. The source attributes it to Brown and notes that it is also conjectured for regularised generalised Feynman integrals of arbitrary scalar Feynman graphs.