   pic: 'overunderbrace-1.gif',
            title: 'Over/under Brace',
            latex: `z = \\overbrace{
\\underbrace{x}_\\text{real} + i
\\underbrace{y}_\\text{imaginary}
}^\\text{complex number}`,
          },

          {
            title: '<kbd>\\hspace</kbd>, positive and negative',
            latex: `A\\hspace{2em}B C\\hspace{-1.5em}D`,
          },
        ],
        'Chemistry': [
          {
            title: 'Chemistry',
            latex: '\\ce{ CrO4^2- }',
          },
          {
        