Wikipedia teaches Spanish poetry

This is accurate, as far as I can tell, and well expresses the muddly nature of what I am learning this month:

In Spanish poetry the meter is the determined by the number of syllables the verse has. Still it is the phonetic accent in the last word of the verse decides the final count of the line. If the accent of the final word is at the last syllable, then the poetic rule states that one syllable shall be added to the actual count of syllables in said line, thus having a higher number of poetic syllables than the number of grammatical syllables. If the accent lies on the second to last syllable of the last word in the verse, then the final count of poetic syllables will be the same as the grammatical number of syllables. Furthermore if the accent lies on the third to last syllable, then one syllables is subtracted from the actual count, having then less poetic syllables than grammatical syllables. Interestingly Spanish poetry uses poetic licenses, unique to romantic languages, to change the number of syllables by manipulating mainly the vowels in the line.

Wikipedia, "Versification"