My web skillz are very old-school.
I only recently learned we're not supposed to use <tt> anymore. (<code> is what the kids use.) We're not supposed to use <a name="whatev"> for our in-document link targets. We should just use <a id="whatev">.
(To be fair, it's pretty cool the targets don't have to be <a> tags any more.)
Anyway, back in my day, to add little icons that might represent your website, we just added a 16x16 pixel /favicon.ico file in some weird, nonstandard Microsoft image format.
Thank you Internet Explorer, the very first evil internet silo that kids these days have never encountered!
My ancient "interfluidity main" site has one of those old-school /favicon.ico files, and I'm not messing with it. But I thought I'd add fresh icons for this site and interfluidity drafts. One 16x16 icon file isn't enough for the modern world. Your site might need an icon on a phone, a tablet, a watch, whatver. Android and Apple devices treat icons differently. Firefox, I discovered, chooses icons differently than other browsers.
The best resource I found to help make sense of the brave new world of website icons was an article by Mathias Bynens.
That article's last update was in 2013, so maybe it's not current? It's a decade newer than my old habits, so hey.
I used Affinity Photo to take the photo I use as an avatar on social media, and label it, for this website as "tech". For prettiness as icons on mobile devices, I also needed to give it rounded corners. I wanted to select a rectangle, round the corners, then invert the selection, and delete to transparent to make rounded corners.
That'a basically what I did, but there's nowhere to set a corner radius on a straight-up rectangualar selection in Affinity Photo.
However, there is a rounded rectangle drawing tool, which draws on its own layer, and — very useful to know! — there is a Selection From Layer menu item, that converts a shape drawn in a layer to a selection. Once I had my selection, invert and delete was no problem and I got my rounded corners.
I gather one can omit rounding corners oneself, if you only care about Apple devices. Apple defines apple-touch-icon and apple-touch-icon-precomposed, and if you supply the not-precomposed version, devices should round corners and maybe drop shadow to "compose" your icon.
Most resources I looked at suggested taking control, so you know what you will get and can use the same icons crossplatform, so that's what I did. So, I rounded my own corners yee-haw!
Then I exported my image as a PNG in all of the sizes recommended by the Bynens article, stole his recommended HTML snippet, and added it — with some modification, see below! — to the main layout of my unstatic-based static-site generators.
<!-- icons / favicons -->
<!-- we just want the squared-corner image with no overlays for traditional favicon uses at tiny sizes -->
<!-- swaldman added, ick, firefox scales down the biggest size for its tab icon, so we use the graphic we want for small sizes as the largest... -->
<link rel="icon" type="image/png" sizes="500x500" href="<( iconLoc.relative )>/interfluidity-wave-blank-square-500x500.png">
<link rel="icon" type="image/png" sizes="32x32" href="<( iconLoc.relative )>/interfluidity-wave-blank-square-32x32.png"> <!-- swaldman added, for standard favicon size -->
<link rel="icon" type="image/png" sizes="16x16" href="<( iconLoc.relative )>/interfluidity-wave-blank-square-16x16.png"> <!-- swaldman added, for standard favicon size -->
<link rel="icon" type="image/png" href="<( iconLoc.relative )>/interfluidity-wave-blank-square-57x57.png"> <!-- swaldman added, for small icons by default -->
<!-- at bigger sizes, we overlay a bit of text -->
<!-- icons as recommened by https://mathiasbynens.be/notes/touch-icons -->
<!-- For Chrome for Android: -->
<link rel="icon" sizes="192x192" href="<( iconLoc.relative )>/interfluidity-wave-tech-192x192.png">
<!-- For iPhone 6 Plus with @3× display: -->
<link rel="apple-touch-icon-precomposed" sizes="180x180" href="<( iconLoc.relative )>/interfluidity-wave-tech-180x180.png">
<!-- For iPad with @2× display running iOS ≥ 7: -->
<link rel="apple-touch-icon-precomposed" sizes="152x152" href="<( iconLoc.relative )>/interfluidity-wave-tech-152x152.png">
<!-- For iPad with @2× display running iOS ≤ 6: -->
<link rel="apple-touch-icon-precomposed" sizes="144x144" href="<( iconLoc.relative )>/interfluidity-wave-tech-144x144.png">
<!-- For iPhone with @2× display running iOS ≥ 7: -->
<link rel="apple-touch-icon-precomposed" sizes="120x120" href="<( iconLoc.relative )>/interfluidity-wave-tech-120x120.png">
<!-- For iPhone with @2× display running iOS ≤ 6: -->
<link rel="apple-touch-icon-precomposed" sizes="114x114" href="<( iconLoc.relative )>/interfluidity-wave-tech-114x114.png">
<!-- For the iPad mini and the first- and second-generation iPad (@1× display) on iOS ≥ 7: -->
<link rel="apple-touch-icon-precomposed" sizes="76x76" href="<( iconLoc.relative )>/interfluidity-wave-tech-76x76.png">
<!-- For the iPad mini and the first- and second-generation iPad (@1× display) on iOS ≤ 6: -->
<link rel="apple-touch-icon-precomposed" sizes="72x72" href="<( iconLoc.relative )>/interfluidity-wave-tech-72x72.png">
<!-- For non-Retina iPhone, iPod Touch, and Android 2.1+ devices: -->
<link rel="apple-touch-icon-precomposed" href="<( iconLoc.relative )>/interfluidity-wave-blank-square-57x57.png">
<!-- end icons / favicons -->
A complication emerged, in that my text-labeled icons looked busy and bad, and the text was illegible, when rendered at very small sizes. So you'll note that, for small sizes, I use interfluidity-wave-blank-square files rather than interfluidity-wave-tech. (I thought the very small icons looked better with square corners as well.)
But Firefox kept picking up the largest <link rel="icon" ... > and downsampling from that, rather than downloading the nearest or nearest-larger icon.
So I added the image I want used only for small icons also as a very large icon.
<link rel="icon" type="image/png" sizes="500x500" href="<( iconLoc.relative )>/interfluidity-wave-blank-square-500x500.png">
Less quirky browsers hopefully never choose this to render from, because there is always a better-sized icon to choose from. But Firefox does choose this one and downsample to render its very small icons-in-a-tab, so the trick gets rid of the ugly, illegibly scaled text in tiny icons under Firefox.
(It does seem a bit wasteful to trick Firefox into downloading 500x500 images to render at 16x16 or 32x32, but if it smartens up, it can download icons prerendered in just those tiny sizes!)
Anyway, that was what I did to add icons to this site and to drafts.
Please let me know if there are much better ways!