Rename "error" to better support external references

The spec includes a definition for the term "error." This is appropriate in the context of the document, but it is too generic for use in other specifications--notably, those that define WebDriver extension commands.

This issue came up in a proposal to define an extension command in the Permissions specification. There, @jyasskin commented:

I'm uncomfortable with WebDriver reserving the term "error" globally.

To be clear: this issue does not interfere with the use case of extension commands. External specifications may reference this document's "error" however they wish. (This is what @jyasskin suggests for the Permissions specification.)

However, that seems like it may become a common enough concern to warrant a change here. As @ato suggested:

Would renaming WebDriver’s error definition to, say, WebDriver error or
something better make WebDriver a better citizen for other specifications to
hook into?

This issue is intended to facilitate discussion about that change. Would the editors be open to a patch which re-named "error" to "WebDriver error"?

Start with the WebDriver specification's definition of “error” and review the linked Permissions discussion for the external-reference concern. Confirm with the editors whether a terminology change is wanted and which replacement is accepted; done means the agreed term is applied consistently throughout the specification and its references.