  Using Grothendieck's "functor of points" approach to algebraic geometry, we
define a new infinite-dimensional algebro-geometric flag space as a $k$-functor
(for $k$ a ring) which maps a $k$-algebra $R$ to the set of certain
well-ordered chains of submodules of an infinite rank free $R$-module. This
generalizes the well known construction of a $k$-functor that is represented by
the classical (i.e. finite-dimensional) full flag scheme. We prove that as in
the finite-dimensional case, there is an action of a general linear group on
our flag space, that the stabilizer of the standard flag is the subgroup $B$ of
upper triangular matrices, and that the Bruhat decomposition holds, meaning
that our space is covered by the disjoint Schubert cells $\text{sh}(B \sigma B)
/ B$ indexed by permutations $\sigma$ of an infinite set. Finally, in the case
of flags indexed by the ordinal $\omega + 1$, we define an analog of the Bruhat
order on this infinite permutation group and prove that when $k$ is a domain,
Ehresmann's closure relations still hold, i.e. that the closure
$\overline{\text{sh}(B \sigma B) / B}$ is covered by the Schubert cells indexed
by permutations smaller than $\sigma$ in the infinite Bruhat order.
