`<big>` and `<span size=''>` acting unexpectedly

[moritztim]

• bar <big>foo</big> bar and bar <span size='[size]'>foo</span> bar render the same as bar foo bar.
• <big>foo</big> bar and <span size='[size]'>foo</span> bar render the same as <big>foo bar</big> and <span size='[size'>foo bar</span>