anchor.diff:  [[internal]]
   ==== `internal`
   
  -This extends not only to `external` and `public` functions, but also `internal` ones: many contracts are meant to be used by inheriting them (e.g. `Pausable`, `PullPayment`, the different `Roles` contracts), and are therefore used by calling these functions. Similarly, since all OpenZeppelin Contracts state variables are `private`, they can only be accessed this way (e.g. to create new `ERC20` tokens, instead of manually modifying `totalSupply` and `balances`, `_mint` should be called).
  +This extends not only to `external` and `public` functions, but also `internal` ones: many contracts are meant to be used by inheriting them (e.g. `Pausable`, `PullPayment`, `AccessControl`), and are therefore used by calling these functions. Similarly, since all OpenZeppelin Contracts state variables are `private`, they can only be accessed this way (e.g. to create new `ERC20` tokens, instead of manually modifying `totalSupply` and `balances`, `_mint` should be called).
   
   `private` functions have no guarantees on their behavior, usage, or existence.
   
  
positive.code: [[libraries]]
  === Libraries
  
  Some of our Solidity libraries use ``struct``s to handle internal data that should not be accessed directly (e.g. `Roles`). There's an https://github.com/ethereum/solidity/issues/4637[open issue] in the Solidity repository requesting a language feature to prevent said access, but it looks like it won't be implemented any time soon. Because of this, we will use leading underscores and mark said `struct` s to make it clear to the user that its contents and layout are _not_ part of the API.
  
  [[events]]
  === Events
  
  No events will be removed, and their arguments won't be changed in any way. New events may be added in later versions, and existing events may be emitted under new, reasonable circumstances (e.g. https://github.com/OpenZeppelin/openzeppelin-contracts/issues/707[from 2.1 on, `ERC20` also emits `Approval` on `transferFrom` calls]).
  
  [[gas-costs]]
  === Gas Costs
  
negative.code: 
  On the https://github.com/OpenZeppelin/openzeppelin-contracts/releases/tag/v2.0.0[OpenZeppelin 2.0 release], we committed ourselves to keeping a stable API. We aim to more precisely define what we understand by _stable_ and _API_ here, so users of the library can understand these guarantees and be confident their project won't break unexpectedly.
  
  In a nutshell, the API being stable means _if your project is working today, it will continue to do so after a minor upgrade_. New contracts and features will be added in minor releases, but only in a backwards compatible way.
  
  [[versioning-scheme]]
  === Versioning Scheme
  