Measurable Function Notation

Question

In a book I'm reading, if $f:\Omega\to X$, is a measurable function, the authors write it is $\mathcal{F}/\mathcal{B}(X)$, where $\mathcal{F}$ is a $\sigma$-algebra over $\Omega$, and $\mathcal{B}(X)$ is the Borel $\sigma$-algebra over induced by the norm topology on $X$, a linear space. I presume that this notation, $\mathcal{F}/\mathcal{B}(X)$, is used to signify that $f$ is measurable with respect to these two topologies, but it's not explicitly stated in the book, nor is it a notation with which I am familiar. Does anyone have a reference for this notation?