This is a sentence with both regular and bold text. It’s in an SVG, inline in the html. This SVG was exported from Adobe Illustrator, and has not been modified afterwards. If you resize this window in any browser but Safari, the text will resize correctly. However, in Safari the spaces between the regular blocks and the bold blocks will vary as you change the window. The reason is that Safari does not smoothly resize text with window size, but steps through a series of jumps, presumably to make the text look good. The result is that if you use SVG to build a web site, and you use real text (not outlines), you have to be careful to avoid using both regular and bold text on the same line. It is unlikely that this will ever change: Apple is deeply committed to their current font-rendering strategy.