Should compounds in a generic reaction be italicised (typography)? As of recent, I provided an answer to the question Law of mass action &amp; collision theory. Therein I wrote a generic reaction

$$\ce{$r_1$R1 + $r_2$R2 + \ldots + $r_n$R_n &lt;=&gt; $p_1$P1 + $p_2$P2 + \ldots + $p_m$P_m}.\tag{1}$$

It seemed natural to write stoichiometric coefficents in Italic, and use upright Roman for the species themselves. 


Italic would be in line with the fact that the coefficients are numbers, and vary with reactions (are different for different transitions).
Upright Roman is how we usually write chemical species, e.g., $\ce{NaCl}$.


Though if I were to overthink, the $\ce{R_$i$}$ would also seem to be variables as such. Since this is a generic reaction, $\ce{R_$i$} \in \{\mathrm{every\ imaginable \ chemical \ species}\}$. Using this logic, I ought to write $(1)$ instead as

$$r_1R_1 + r_2R_2 + \ldots + r_nR_n \ce{&lt;=&gt;} p_1P_1 + p_2P_2 + \ldots + p_mP_m.\tag{1'}$$




Is there an official example or guideline how to handle this situation?


Personally I wholeheartedly support option $(1)$ but is this what is recommended?


What about the subindices? Upright or Italic?


Note that this qualitatively differs from Proper typography of “$\ce{NO_x}$”. There the number of elements actually changes within a chemical species (marks the number of carbons in alkanes for example) whereas here it is more for labelling purposes.
Going by the basic rule of a variable (that can hold multiple values) being italic, I would go for the $r_nR_n$ style (4 times italics), but then I found the following in the IUPAC Green Book (printed page 53):


  $$0 = \sum_j \nu_j \mathrm{B}_j \quad \text{where }\mathrm{B}_j\text{ denotes a species in the reaction ...}$$


Here, the B is upright although it is definitely a placeholder. I don't understand, why.

For the subindices, I think (hope) there is no doubt that the $n$ and $m$ should be italic, because they clearly are variables standing for numbers (either any number as in the sum, or for an unknown maximum number $1, 2, 3, \ldots, n$ as in the generic reaction). Both form are well established in mathematics (and I hope chemists don't deviate).



The IUPAC Gold Book, R05156 uses the same convention.


  For the general chemical reaction :
  $$a\,\mathrm{A} + b\,\mathrm{B} \rightarrow p\,\mathrm{P} + q\,\mathrm{Q} + \dots% not using \ce to have proper formating regardless of mhchem version$$


And they do not mean Boron and Phosphorus.

(Spotted via this answer).