error[markdown-refs]: references to proposals with a `category` of `ERC` must use a prefix of `ERC`
  --> input.md
   |
18 | This is the motivation for the EIP, which extends [EIP-721](./eip-721.md).
   |
error[markdown-refs]: references to proposals without a `category` must use a prefix of `EIP`
  --> input.md
   |
21 | This is the specification for the EIP, which doesn't extend [EIP-123](./eip-123.md) or [ERC-123](./eip-123.md).
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error[markdown-refs]: references to proposals with a `category` of `ERC` must use a prefix of `ERC`
  --> input.md
   |
24 | This is the rationale for the EIP-721.
   |