As per the book "General, Organic, and Biological Chemistry" by H. Stephen Stoker; the following can be said.
A special case of electron sharing exists in which one atom participating in a covalent bond supplies two electrons to the bond and the other atom supplies zero electrons to the bond. This can occur when one atom, the donor, has a nonbonding pair of electrons and the other atom, the acceptor, has two vacancies in its valence electron shell. Bonds of this type are called coordinate covalent bonds. A coordinate covalent bond is a covalent bond In which both electrons in a shared pair of electrons come from one of the two atoms in the bond.
The molecule HOCIO (HCIO2) is an example of a coordinate-covalent-bond-containing molecule. Its formation can be envisioned as resulting from the addition of an oxygen atom. which has six valence electrons, to a HOCI molecule.
Combining these two entities together produces the HOClO molecule through coordinate covalent bond formation that involves the Cl atom of HOCl and the new O atom.
You can have a look at this extract from the book.