\documentclass[a4paper]{article}

\usepackage{pgfplots}

\usepackage{pgfplots.assert}

\begin{document}

\begingroup
	\pgfplotsset{mesh/color input=explicit}%
	\pgfplotsassertequalstok{explicit symbolic}{\pgfplotspointmetainputhandler}{}
\endgroup

\begingroup
	\pgfplotsset{
		point meta=f(x),
		mesh/color input=explicit,
	}%
	\pgfplotsassertequalstok{explicit symbolic}{\pgfplotspointmetainputhandler}{}
\endgroup

\begingroup
	\pgfplotsset{
		point meta/symbolic={abc},
		mesh/color input=explicit,
	}%
	\pgfplotsassertequalstok{TeX code symbolic}{\pgfplotspointmetainputhandler}{}
\endgroup
\end{document}

