If, for some reason, one character gets more of the loot, such as a thief stealing gems from the saddle bags on the way home, then he should get the additional experience points.Again, this passage rings a lot of bells for me, since it's how I used to play back in the day. It seems to be unique to Holmes, or at least it doesn't seem to derive from anything in the LBBs, but someone can correct me if I'm wrong on this score. That said, Holmes also allows for the referee to lower the number of XP awarded to duplicitous characters, such as one who "sneaks out of the dungeon with all the treasure while the rest of the party is being eaten." Holmes reiterates OD&D's prohibition against gaining more than one level at a time, regardless of how much XP is earned in an adventure. He also clarifies how hit points are determined, thereby denying that the approach taken in Empire of the Petal Throne is in fact normative. Further thoughts on Holmes and XP can be read here.
The XP charts for character classes in Holmes are interesting. The required XP per level for each of the four classes is the same as in OD&D and hit dice are as per Greyhawk. Level titles are present but not explained (and a 3rd-level cleric is now merely a "priest," as opposed to "village priest."). Magic-user spell progression has changed slightly at 3rd level, with such characters now getting only two 1st-level spells and one 2nd-level spell rather than three 1st-level spells and one 2nd-level one. Thief abilities are identical to those in Supplement I (i.e. no find traps ability) and at the same percentages. Thieves of 3rd level and above are noted as being able to "read magic scrolls and books," in addition to "80% of languages," which is a bit confusing compared to Greyhawk. One could make the case that Holmes was allowing 3rd-level thieves to cast spells from scrolls, but I rather suspect what he wrote is the result of an imprecision in his text rather than changing the circumstances under which thieves can cast spells. Thieves are explicitly given exactly one chance per level to open a specific lock. If they fail, they cannot try again until their chance to succeed increases.
Most fascinating of all is that elves are listed as sharing the same experience table as fighting men, halflings, and dwarves, but are not also listed under the table for magic-users. This is particularly strange given that he notes in a paragraph below the tables that elves "progress in two areas" and "use a six-sided die for hits." Halflings, meanwhile, though fighting men, use only a D6 per level for hit points.
Clerical turning works identically to OD&D, using the exact same chart. It also retains OD&D's 2d6 roll to determine the number of undead turned rather than the number of hit dice turned, as in Moldvay (which, in this case, is the outlier, as AD&D more or less follows OD&D on this point).
The many meanings of "level" are discussed at some length, but without anything that won't be repeated again and again over the years. Holmes lays down the classical form of this discussion.