Link to the Format Specification Mini Language section from f-strings' documentation.
Top-level format specifiers may include nested replacement fields.
These nested fields may include their own conversion fields and
-format specifiers, but may not include more deeply-nested replacement fields.
+:ref:`format specifiers <formatspec>`, but may not include more
+deeply-nested replacement fields.
Formatted string literals may be concatenated, but replacement fields
cannot be split across literals.