This highly depends on how a given string is interpreted and which comparison function is used. 

Traditionally, a string is a sequence of characters. For example, one could subdivide a given string into a list of elements like tokens or single characters. Let's assume the string is subdivided into a list of characters and the comparison function compares two characters and decides which character comes first in the alphabet. If the characters in the given string were sorted alphabetically, then binary search would be possible.
spam fails_task lang_mismatch pii not_appropriate hate_speech sexual_content quality toxicity humor helpfulness creativity violence