Bessel function, what does the notation in this function mean?

Hello,

I have come across the following equation and want to know what the notation means exactly:

$$\frac{-2 \pi \gamma}{\sigma} \frac{[ber_2(\gamma)ber'(\gamma) + bei_2(\gamma)bei'(\gamma)]}{[ber^2(\gamma) + bei_2(\gamma)]}$$

Now, I know ber is related to bessel functions. For example, I think ber is the real part of the Bessel function of first kind, and bei might be the imaginary part? I assume ber' is the derivative

Could someone possibly explain what each of the bei ber parts are?

I ultimately will want to calculate this formula in Matlab. Matlab's bessel function can apparently return different orders of the bessel function, should I be using anything other than order 1? does the subscripted 2 in the formula indicate order 2 should be used for instance? Alternatively, should I be using multiple orders and summing the results or something like this to improve accuracy?

Thanks!