Change exception identifier to avoid confusion with SPDX spec

[silverhook]

REUSE specs 2.0 currently refers to the following tags:

• Valid-License-Identifier to tag the actual text of a license (and License-Text to include a copy of its text)
• SPDX-Exception-Identifier to tag the actual text of an exception (and Exception-Text to include a copy of its text)

While the license identifier tag was already changed in order not to clash with the SPDX spec’s own tags, the exception tag was not updated to match it. This can cause confusion.

I would suggest that we also change the license exception tag from SPDX-Exception-Identifier to Valid-Exception-Identifier.

For more info, see discussion on SPDX Legal mailing list.

[mxmehl]

Is this solved in REUSE 3.0?

[carmenbianca]

No longer relevant in REUSE 3.0