EDIT: after reading egreg's comment, changing from \sqrt[3]{x} to \root 3 \of{x}, to indicate using plain TeX, not LaTeX
Consider $$\sqrt{x}$$ vs $$\root 3 \of{x}$$.
The latter has a 'root' of 3.
How do we typeset this?
On page 443 of the TeX Book, rule 11, it describes typesetting the radical atom: \radcal and \sqrt. However, it only describes "root-less" types, like \sqrt{x}, and not the ones with a root, like \root 3 \of{x}
Question: how is the root/3 in a sqrt typeset?
\root 3\of{x}. The TeXbook, page 130 (bottom). Do you mean you want a description of how LaTeX implements\sqrt[3]{x}? – egreg Sep 20 '17 at 10:26\newbox\rootbox. – egreg Sep 20 '17 at 10:53