Existing Wording
The resource bundle mostly includes the whole content of a resource.

Proposed Wording
The resource bundle mostly includes the whole content of its group of resources.

(Replace "mostly includes" with clearer explanation)

Comments
Confusing statement in two ways. The previous sentence had just said a bundle contains a collection of resources, but then this sentence refers to "a" resource. "Mostly includes" is undefined and unclear. Does this mean that parts of some resources are not included? Does it mean that the bundle contains resources in their entirety PLUS additional "bundle-specific data?" Depending on what is meant, suggest rewording to make it clearer.

Grahame's Comments
just remove the sentence. I don't have a clue what it's trying to say