2. "Such as" meaning "Of a kind that; like": for example
I have no other information than such as is presented to me in this letter.
In this instance, the implication is something like
I have no other information than [information of] such [a kind] as [i.e. "that" or "which"] is presented to me in this letter.
3. "Such as" meaning "Those who": for example
Such as read this letter will learn of its contents.
The meaning here is to be derived from expanding the sentence in more or less this way:
[Those people of] such [a kind] as [again, sc. "that" or better "who"] read this letter will learn of its contents.
In other words, in both cases the "such" is acting as a nominal, more like a noun than like an adjective, and refers either to a previous noun (as in the first sentence, where it refers to "information") or to an implied noun (as in the second sentence, where the noun "people" can be inferred from the verbs "read" and "learn").