  We have recently shown that critical Anderson electron in $D=3$ dimensions
effectively occupies a spatial region of infrared (IR) scaling dimension
$d_\text{IR} \approx 8/3$. Here we inquire about the dimensional substructure
involved. We partition space into regions of equal quantum occurrence
probability, such that points comprising a region are of similar relevance, and
calculate the IR scaling dimension $d$ of each. This allows us to infer the
probability density $p(d)$ for dimension $d$ to be accessed by electron. We
find that $p(d)$ has a strong peak at $d$ very close to 2. In fact, our data
suggests that $p(d)$ is non-zero on the interval $[d_\text{min}, d_\text{max}]
\approx [4/3,8/3]$ and may develop a discrete part ($\delta$-function) at $d=2$
in infinite-volume limit. The latter invokes the possibility that combination
of quantum mechanics and pure disorder can lead to emergence of topological
dimensions. Although $d_\text{IR}$ is based on effective counting of which
$p(d)$ has no a priori knowledge, $d_\text{IR} \ge d_\text{max}$ is an exact
feature of the ensuing formalism. Possible connection of our results to recent
findings of $d_\text{IR} \approx 2$ in Dirac near-zero modes of thermal quantum
chromodynamics is emphasized.
