## The current behavior

The full value of the `key` is very difficult / impossible to find and use in the interface of the React Devtools.

![Kapture 2020-04-22 at 11 47 47](https://user-images.githubusercontent.com/1935696/79997715-25222680-84ba-11ea-97ba-51f1679a8c91.gif)

Only managed to find it by accident :(

## The expected behavior

The `key` is visible in the props list to the right.

### Detailed Proposal

As mentioned below in https://github.com/facebook/react/issues/18702#issuecomment-617924196

Add a light divider and new section in the props panel to the right.

Potentially also add a question mark that shows an explanation about the fact that things in this section are not really props.

Ref (Original implementation): https://github.com/facebook/react-devtools/pull/328
)}
            </Fragment>
          )}
        </ContextMenu>
      )}
    </Fragment>
  );
}
function formatSourceForDisplay(fileName: string, lineNumber: string) {
  const BEFORE_SLASH_RE = /^(.*)[\\\/]/;
  let nameOnly = fileName.replace(BEFORE_SLASH_RE, '');
  
  
  if (/^index\./.test(nameOnly)) {
    const match = fileName.match(BEFORE_SLASH_RE);
    if (match) {
      const pathBeforeSlash = match[1];
      if (pathBeforeSlash) {
        const folderName = pathBeforeSlash.replace(BEFORE_SLASH_RE, '');
        nameOnly = folderName + '/' + nameOnly;
      }
    }
  }
  return `${nameOnly}:${lineNumber}`;
}
type SourceProps = {|
  fileName: string,
  lineNumber: string,
|};
function Source({fileName, lineNumber}: SourceProps) {