[FIX] Update HED appendix to comply with current HED version

[VisLab]

The HED.md appendix has been rewritten to use the current version of HED.

Please review:
@sappelhoff @dungscout96 @happy5214 @tpatpa @smakeig @dorahermes @IanCa @arnodelorme @Remi-Gau

[VisLab]

I noticed that the link checker failed on the glossary section, which is not part of this pull request. Perhaps someone could address?

[sappelhoff]

Thanks! I like the revamp - it's more concise and clear. I left a couple of comments.

[sappelhoff]

I noticed that the link checker failed on the glossary section, which is not part of this pull request. Perhaps someone could address?

@VisLab we have to ignore the LinkChecker for now, unfortunately (technical detail, see this comment and the six that follow: #892 (review) )

[Remi-Gau]

I had a quick look and this seems like a clearer and concise "intro" to HED.

[dorahermes]

Very clear!! I only had one small question on whether there are any previous BIDS examples that use the long form. If there are existing BIDS examples with the long form, it would make sense to have one example that uses both the long and short forms, while stating that the short form is recommended.

If there are no BIDS examples with the long form, this looks good to me!

[dorahermes]

lgtm

[sappelhoff]

@VisLab thanks for addressing most of my suggestions. A few were left open and I simply committed those that I deemed uncontroversial, for the diff see: 0cf0835

I can revert that commit if you disagree.

That leaves only one "controversial" point from my review open:

• You often refer to "tools" that "do something" ... I made some suggestions to change this throughout the appendix to "HED specific tools" that "MUST do this and that" (... implicitly meaning that HED tool must behave in that way)
• I find that language more clear: If you agree, feel free to accept these remaining suggestions, else I'd appreciate if you could suggest an alternative, so that we can more precisely talk about these "tools" (this was also a frequently raised point in recent HED paper reviews)

PS: if you missed my remaining suggestions because they were so many, you need to click on the "load more", or go to the files changed overview: https://github.com/bids-standard/bids-specification/pull/970/files

[sappelhoff]

LGTM!

[sappelhoff]

Thanks for the update, Kay. And thanks for the reviews everyone else - I am merging this now.