Each PR that contributes to docs will generate a unique (to that PR) URL to preview the PR live for review.

We have chosen Netlify as the host and to build locally via Github Actions instead of offloading to Netlify (imposes limit in monthly minutes).

A separate action handles creating/updating the deployment comment. It provides a custom message and is portable should the deploy preview action change in future.

To support previews from non-collaborators PR contributions, we cannot rely on secrets access from workflows triggered by the `pull_request` event.

To do so securely, according to official advice from Github, we must run the third-party contribution in the restricted `pull_request` context, and then use a 2nd workflow to deploy the build (which requires secrets access).

Better naming convention for documentation workflows.

Split workflow only indicated status on PR of the 1st stage (building the preview to deploy), not the deployment progress/result. This needs to be managed more directly until the action better supports split-workflow scenario.

This would be more ideal on the 2nd phase workflow (`workflow_run`), however keeping it simple for now.

Limits the concurrency of the initial pull request workflow for documentation contributions that have PRs with multiple event triggers in a small time span (before the workflow triggered would complete). The main benefit is to avoid redundant deploys if the initial workflow has been triggered again to build the PR once more. It only will work against concurrent workflows for that PR in the 1st stage, if an existing `workflow_run` (2nd stage) is active for that PR it will not be cancelled.

A requirement from Netlify for the [sponsored OSS organization plan](https://www.netlify.com/legal/open-source-policy).

Production and Deploy Preview builds are now maintained via the same shell command, so version updates of docker image is in one place.

Additionally deletes unnecessary build output which upstream provides no support to exclude.

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update-versions-json script minor fix to meet style guidelines.

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Minor comment correction in docs production deploy workflow.

This is used by the preview deploys on Netlify. Production deploys on Github Pages require a top-level 404 page manually deployed (since all are deployed to a version subpath).

This 404 page was custom built and optimized by me. This is the final minified output, separate source to build is available if needed. All content is inlined into the document except the large bg image. It compresses down to about 4KB with gzip/brotli when delivered over network.

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Likewise the `favicon.ico` is a fallback for browsers that implicitly check the domain root for this file if the SVG isn't supported/preferred. Browsers check for this file without it being present in the HTML head meta elements.

On Github Pages the `favicon.ico` isn't likely to be picked up by even top-level as typical deployment has the project name as a subpath. The docs however reference a PNG favicon which should be widely supported.

The `favicon.ico` was generated by RealFaviconGenerator online tool with SVG source input. It contains 16px, 32px and 48px sizes. Quality is better than the `favicon.io` generator.

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Minor quote style consistency fix in mkdocs.yml. Also added trailing slash to site_url, which was required in the past to avoid some 404 support errors but should be resolved now with latest mkdocs.

SVG source cleaned up and optimized with SVGO 2.3.

Minified versions (`.min.svg` extension) remove unnecessary data and white-space to reduce size further for production use. This extension better differentiates by filename that it's different from the `src` version.

PNGs updated to match minor differences from optimizations (reduced float precision).

`mkdocs build` will exclude directories that are prefixed with a `.`. There's no need for these files to be deployed each time.