The roburic tilde It is the one that goes over the closed vowel when it is tonic and is preceded or followed by an open vowel. The tilde is a mark that indicates the greatest voice force in a syllable. Its use is quite restricted, therefore it is not used in most of the words.
On the other hand, a stressed vowel is the nucleus of a stressed syllable, that is, one that is perceived as the most prominent within a word. This class of tilde is also known as absolute tilde or hyatic tilde.
The particular combination of a closed or weak vowel (i, u) stressed and an open or strong vowel (a, e, o) forms a hiatus. When two contiguous vowels are pronounced in two different syllables, a hiatus occurs.
The Royal Spanish Academy (RAE) defines the syllable as a unit of the language composed of one or more articulated sounds grouped around the loudest, generally a vowel.
The purpose of the roburic tilde is to break the diphthong so that they are pronounced in two strokes of the voice (two syllables).
The norm expresses that, without exception, any hiatus that is formed by a strong vowel and a weak tonic must be marked, regardless of the order of the vowels..
The possible combinations would be ía, íe, ío, úa, úe and úo when the open vowel goes first, and aí, eí, oí, aú, eú and oú when it goes after.
It should be taken into consideration that the letter h does not break the hiatus, therefore the same rule should be applied in these cases. Likewise, a hiatus can occur with two equal vowels, or two open vowels..
But in those cases the general rules of accentuation are used. These general rules are also taken into account when the tonic element is the open vowel.
Below are two excerpts from works by the Colombian writer Gabriel García Márquez. The blush accents are underlined for identification.
1-Many years later, in front of the firing squad, Colonel Aureliano Buendía had to remember that remote afternoon when his father took him to know the ice.
Macondo was then a village of twenty houses of mud and cañabrava built on the shore of a River of waters diaphanous that were rushing down a bed of polished stones, white and huge as prehistoric eggs. The world was so recent that many things they lacked by name, and to mention them you had to point your finger at them.
(Excerpt from One Hundred Years of Solitude)
2-Servant Mary not understood never what happened to Cayetano Delaura, why not went back with its basket of beauties of the portals and its insatiable nights. May 29, without breath for more, went back dreaming of the window of a snowy field, where Cayetano Delaura was neither would come back to never be.
I had in his lap a bunch of golden grapes that they came back to sprout as soon as they are I used to eat. But this time he did not pluck them one by one, but two by two, barely breathing because of the desire to beat the bunch to the last grape..
(Excerpt from Of love and other demons)