Example: $p\text{-}\mathrm{XC}{\phantom{A}}_6\mathrm{H}{\phantom{A}}_4\mathrm{Y}$, where an electron pair can be delocalized from electron-donating $\mathrm{X}$ not only to ring carbons but also to electron-withdrawing $\mathrm{Y}$.

Notes:

1. This may be contrasted with cross-conjugation.
2. In Hammett-type correlations (linear Gibbs-energy relationships), this situation can lead to exalted substituent constants ${\sigma }^{+}$ or ${\sigma }^{-}$, as in solvolysis of $p\text{-}\mathrm{CH}{\phantom{A}}_3\mathrm{OC}{\phantom{A}}_6\mathrm{H}{\phantom{A}}_4\mathrm{C}(\mathrm{CH}{\phantom{A}}_3){\phantom{A}}_2\mathrm{Cl}$ or acidity of $p\text{-}\mathrm{nitrophenol}$, respectively.