Problem in template processing?

[JetForMe]

I tried adding the static file template processor for some simple variable substitution, and it seems to corrupt my CSS files. The example shows returning emptyString when a variable name doesn’t match, but in my CSS it's finding everything delimited by %, meaning something like

    --pico-font-size: 100%;
    --pico-text-underline-offset: 0.1rem;
    --pico-border-radius: 0.25rem;
    --pico-border-width: 0.0625rem;
    --pico-outline-width: 0.125rem;
    --pico-transition: 0.2s ease-in-out;
    --pico-spacing: 1rem;
    --pico-typography-spacing-vertical: 1rem;
    --pico-block-spacing-vertical: var(--pico-spacing);
    --pico-block-spacing-horizontal: var(--pico-spacing);
    --pico-grid-column-gap: var(--pico-spacing);
    --pico-grid-row-gap: var(--pico-spacing);
    --pico-form-element-spacing-vertical: 0.75rem;
    --pico-form-element-spacing-horizontal: 1rem;
    --pico-group-box-shadow: 0 0 0 rgba(0, 0, 0, 0);
    --pico-group-box-shadow-focus-with-button: 0 0 0 var(--pico-outline-width) var(--pico-primary-focus);
    --pico-group-box-shadow-focus-with-input: 0 0 0 0.0625rem var(--pico-form-element-border-color);
    --pico-modal-overlay-backdrop-filter: blur(0.375rem);
    --pico-nav-element-spacing-vertical: 1rem;
    --pico-nav-element-spacing-horizontal: 0.5rem;
    --pico-nav-link-spacing-vertical: 0.5rem;
    --pico-nav-link-spacing-horizontal: 0.5rem;
    --pico-nav-breadcrumb-divider: ">";
    --pico-icon-checkbox: url("data:image/svg+xml,%3Csvg

becomes

    --pico-font-size: 1003Csvg

But it seems to limit parameter names, so simply returning the variable name doesn't work either, as it still doesn't then result in an unmodified file.

Looking at the template processing code there’s a comment that suggests a double percent (%%) is an escaped percent, but this is hugely burdensome in a CSS file (for example).

The template processor should instead use a less likely delimiter (say %%), and if it doesn’t find the closing delimiter with some reasonable number of characters (say, 32), leave the content intact (and don’t call the template processor func).

Should I write this up, or am I missing something obvious?

(BTW another discussion says you won't be enhancing this at all, but if all you need is simple variable substitution, it would be nice not to have to bring in a whole other thing. But as-is, I don't think this works at all.)