Clarify that pessimistic/optimistic concurrent are approaches, not settings
In testing analyzers, add note about ignoring the token "type"
Add more context to mappings and custom mappings
"must -> should" in bool query explanation
Clarified missing/exists and IS_NULL
Bool query - converted para to tip
Added link to Controlling Relevance to relevance intro
Converted all [IMPORTANT] to another annotation type
Formatting
Added sidebar to the intro giving back story of ES