Ensure logo-nhs.svg is a valid SVG file.

[codebymikey]

Add the xlink namespace to address the 'Unbound namespace prefix: "xlink"' error.

Description

The SVG is currently not valid.

Checklist

• Tested against our testing policy (Resolution, Browser & Accessibility)
• Follows our coding standards and style guide
• CHANGELOG entry

[chrimesdev]

Hey @codebymikey thanks for opening this pull request.

Do you have a bit more information about the error you were getting so I can understand the context of this change? Where are you getting the 'Unbound namespace prefix: "xlink"' error?

We are aware of some issues affecting HTML validation with the fallback png logo (#572) but this doesn't seem to be related.

[codebymikey]

I just noticed that the file wasn't valid in general (none of the svg viewers I found online could open it), see Github's own SVG preview breaking:
https://github.com/nhsuk/nhsuk-frontend/blob/e3850ef/packages/assets/logos/logo-nhs.svg
vs
https://github.com/nhsuk/nhsuk-frontend/blob/28c9253/packages/assets/logos/logo-nhs.svg

Viewing the svg directly in Chrome spits out an error message regarding the namespace prefix, but still manages to render.

The error I referenced in particular was coming from running the assets through gulp-image's svgo optimizer which apparently uses sax-js under the hood:

https://github.com/isaacs/sax-js/blob/5aee2163d55cff24b817bbf550bac44841f9df45/lib/sax.js#L809-L813

[chrimesdev]

Thanks @codebymikey that makes sense - I'm surprised we haven't spotted this before!

The change looks good but there are a couple of other places that we'll need to make this change;

Header component template file (Line 17) https://github.com/nhsuk/nhsuk-frontend/blob/master/packages/components/header/template.njk#L17

Header component template file (Line 28) https://github.com/nhsuk/nhsuk-frontend/blob/master/packages/components/header/template.njk#L28

Header component README file (There are a couple of places here) https://github.com/nhsuk/nhsuk-frontend/blob/master/packages/components/header/README.md

We'll need a CHANGELOG entry too under 4.0.1 as a fix - though we can pick this up if you prefer.

Thanks again.

[codebymikey]

Applied the namespace to all known instances of xlink in the codebase.

I'll leave the CHANGELOG part to you guys to handle.

[chrimesdev]

Thanks @codebymikey looks good, I'll update the CHANGELOG before the next release