Observe the following examples. In all of them there is the maximum number of non-cumulative double bonds, and there is also a ring atom linked to neighboring atoms only by single bonds. If that atom also has one (or two) hydrogen atoms, that hydrogen (or one of the two) receives the name of indicated hydrogen, and must be stated in the name.

indicated hydrogen 01

[1] A pyrrole heterocycle that has the largest possible double bonds, but lacks a double bond on the phosphorous atom. This fact must be indicated in the name through the hydrogen indicated in position 1. (1H-Pyrrole)

[2] Pyrrole heterocycle with the largest double bonds. The lack of double bond in position three should be reflected in the name (3H-Pyrrole)

[3] Pyrane heterocycle with hydrogen indicated in position 4. (4H-Pyrane)

[4] Dithiine heterocycle, with maximum double bonds, but with two saturated carbons that should be reflected in the name (2H,4H-1,3-dithiine)

indicated hydrogen 02

[5] Dithiozine heterocycle, with the maximum possible double bonds, but with saturated carbons in 2,6 positions that should be reflected in the name (2H,6H-1,5-Dithiozine)

[6] Dithiozine heterocycle missing a double bond between the 2,3 positions. (2,3-Dihydro-1,4-dithiozine)

[7] Phosphepine heterocycle, with the maximum possible double bonds. The saturated carbon of position 4 is indicated in the name. (4,4-Dimethyl-4H-phosphepine)

Finally, there are occasions in which indicated hydrogens and formal hydrogenations of double bonds coexist in the same molecule. The numbering (once the minor locants have been given to the heteroatoms as a whole) continues so that the lowest locants also correspond to the H listed first and to the hydro prefixes later. The correct sequence of the different parts that make up the global name of a heterocycle are: 1/ the non-Hantzsch-Widman prefixes (in alphabetical order), except for hydro; 2/ the prefixes hydro; 3/ the H indicated; 4/ the Hantzsch-Widman name of the fundamental heterocycle.
indicated hydrogen and hydros
[8] Selenine heterocycle, we indicate the three carbons saturated with dihydro (lack of a double bond) and hydrogen indicated. (3,4-Dihydro-2H-selenine)
I Note that the indicated hydrogen has preference in the numbering of the heterocycle and we assign it the lowest locant.
[9] Azepine heterocycle, the heterocycle can contain a maximum of three double bonds, we indicate the lack of one of them with dihydro. There is still a third saturated atom (nitrogen) that we mark with indicated hydrogen. (2,5-Dihydro-1H-azepine)
[10] Dithiozine heterocycle, has a dihydro and two indicated hydrogens. (7-Ethyl-3-methyl-3,4-dihydro-2H,6H-1,5-dithiozine)