....
        startup: {
		// MathJax creates anchor tags from MathML elements with href attributes.
		// But it does not add the title attributes from these elements
		// that we need for the extension Popups
		ready() {
			const { MML } = window.MathJax._.core.MmlTree.MML;
			MML.a = MML.mrow;
			const { ChtmlWrapper } = window.MathJax._.output.chtml.Wrapper;
			ChtmlWrapper.prototype.handleHref = function ( parents ) {
				if ( !this.node.attributes.hasExplicit( 'href' ) ) {
					return parents;
				}
				const attrs = { href: this.node.attributes.get( 'href' ) };
				if ( this.node.attributes.hasExplicit( 'title' ) ) {
					attrs.title = this.node.attributes.get( 'title' );
				}
				return parents.map(
					( parent ) => this.adaptor.append( parent, this.html( 'a', attrs ) )
				);
			};
			const { SvgWrapper } = window.MathJax._.output.svg.Wrapper;
			SvgWrapper.prototype.handleHref = function ( parents ) {
				const href = this.node.attributes.get( 'href' );
				if ( !href ) {
					return parents;
				}

				const defineOffsetGetter = ( target, key, rectKey ) => {
					if ( typeof target[ key ] !== 'undefined' ) {
						return;
					}
					Object.defineProperty( target, key, {
						get: () => {
							const rect = target.getBoundingClientRect && target.getBoundingClientRect();
							return rect && Number.isFinite( rect[ rectKey ] ) ? rect[ rectKey ] : 0;
						}
					} );
				};
				const attrs = { href };
				if ( this.node.attributes.hasExplicit( 'title' ) ) {
					const title = this.node.attributes.get( 'title' );
					attrs[ 'data-title' ] = title;
					attrs.title = title;
				}
				let index = 0;
				const isEmbellished = this.node.isEmbellished && !this.node.isKind( 'mo' );
				return parents.map( ( parent ) => {
					parent = this.adaptor.append( parent, this.svg( 'a', attrs ) );
					const { h, d, w } = isEmbellished ? this.getOuterBBox() : this.getLineBBox( index );
					const dom = this.dom[ index ];
					const rect = this.svg( 'rect', {
						'data-hitbox': true,
						fill: 'none',
						stroke: 'none',
						'pointer-events': 'all',
						width: this.fixed( w ),
						height: this.fixed( h + d ),
						x: index === 0 || isEmbellished ? this.fixed( -this.dx ) : 0,
						y: this.fixed( -d )
					} );
					this.adaptor.append(
						dom,
						rect
					);
					defineOffsetGetter( parent, 'offsetWidth', 'width' );
					defineOffsetGetter( parent, 'offsetHeight', 'height' );
					index++;
					return parent;
				} );
			};
			window.MathJax.startup.defaultReady();
		},
		// See https://phabricator.wikimedia.org/T375932 and the suggested fix from
		// https://github.com/mathjax/MathJax/issues/3292#issuecomment-3487698042
		// Makes rendering of \matcal look similar to the browsers MathML rendering
		// and the old image rendering.
		// Note that \mathsrc (which is unsupported by texvc) would map to the
		// same unicode chars and thus should not be activated.
		pageReady() {
			const font = window.MathJax.startup.document.outputJax.font;
			Object.assign( font, {
				fontLoadDynamicFile: font.loadDynamicFile,
				async loadDynamicFile( dynamic ) {
					await this.fontLoadDynamicFile( dynamic );
					if ( dynamic.file === 'script' ) {
						await this.fontLoadDynamicFile( this.constructor.dynamicFiles.calligraphic );
						const variant = font.variant;
						const map = { 1: 0x212C, 4: 0x2130, 5: 0x2131, 7: 0x210B, 8: 0x2110, 11: 0x2112, 12: 0x2133, 17: 0x211B };
						window.MathJax.config.remapChars( variant.normal, variant[ '-tex-calligraphic' ], 0x1D49C, map, 'C' );
						window.MathJax.config.remapChars( variant.normal, variant[ '-tex-bold-calligraphic' ], 0x1D4D0, {}, 'CB' );
					}
				}
			} );
			return window.MathJax.startup.defaultPageReady().then( () => {
			} );
		},
		output: 'svg'
	}
``` The code is a bit more complicated because there was a positioning bug of the preview, similar to the one from T381311.