Most sites that present Unicode character information will list only what is in the character properties database. (In particular, such sites rarely inform about any prose within the Unicode standard that may be relevant.)
The clue in those properties that suggests there is more to the story about U+0340 and U+0341 is that they have singleton canonical decompositions to U+0300 and U+0301, respectively. Such decompositions mean there is no behavior difference between, for example U+0341 and U+0301, which raises the question of why are they in the standard and thus there must be more info about them. Time to look in the prose.
FYI, the excerpt Victor quoted can be found in https://www.unicode.org/charts/nameslist/n_0300.html or the charts at https://www.unicode.org/charts/PDF/U0300.pdf