Rolled Rs -- according to the Spanish Royal Academy

1. Use a soft R when a single R precedes a vowel (cara) or a consonant (perla).
   Use a rolled R when there are 2 consecutive Rs (villarreal).

2. Use a rolled R when a word starts with a single R (rosa).

3. Use a rolled R when a single R is preceded by AB (abrogar), OB (obrepción), or SUB
(subrayar).

4. Use a rolled R when a single R is preceded by PRE (prerogativa) or PRO (prorata).

5. Use a rolled R when a single R is preceded by L (malrotar), N (enredo), or S
(israelíta).

6. Use a rolled R when a word is composed of two words, the second of which starts with
only one single R (boquirubio).