  In this paper we construct Ritz-type projectors with boundary interpolation
properties in finite dimensional subspaces of the usual Sobolev space and we
provide a priori error estimates for them. The abstract analysis is exemplified
by considering spline spaces and we equip the corresponding error estimates
with explicit constants. This complements our results recently obtained for
explicit spline error estimates based on the classical Ritz projectors in
[Numer. Math. 144(4):889--929, 2020].
