  The global analogue of a Henselian local ring is a Henselian pair: a ring A
and an ideal I which satisfy a condition resembling Hensel's lemma regarding
lifting coprime factorizations of polynomials over A/I to factorizations over
A. The geometric counterpart is the notion of a Henselian scheme, which is an
analogue of a tubular neighborhood in algebraic geometry.
  In this paper we revisit the foundations of the theory of Henselian schemes.
The pathological behavior of quasi-coherent sheaves on Henselian schemes in
characteristic 0 makes them poor models for an "algebraic tube" in
characteristic 0. We show that such problems do not arise in positive
characteristic, and establish good properties for analogues of smooth and
\'etale maps in the general Henselian setting.
