Official resource for Spanish related doubts (words, grammar, orthography, pronunciation, ect.): Royal Spanish Academy
The official resource for any Spanish learning student to consult any doubt weather it's orthography, phonetics, grammar, etymology, word meaning, is "La Real Academia Española" or the Royal Spanish Academy. It is: (Spanish) "es una institución con personalidad jurídica propia que tiene como misión principal velar por que los cambios que experimente la lengua española en su constante adaptación a las necesidades de sus hablantes no quiebren la esencial unidad que mantiene en todo el ámbito hispánico" (English) "it's an institution with a juridic personality which has as a main mission to ensure that the changes that the Spanish language experiments in it's constant adaptation to the necessities of its speakers doesn't break the essential unity that's maintained in all the Hispanic environment".
In summary it's an institution that documents the changes, due to the necessities of Spanish speakers, in this language and to maintain the essential links that bond every Spanish speaking country in the world.
The site offers an official Spanish dictionary, a pan-Hispanic (all Hispanic) dictionary of doubts, their official grammar and orthography resources to consult them for orientation, and many other resources to have total knowledge of this beautiful language. Obviously ALL OF IT IS IN SPANISH.
It's not a "rule-setter" to restrain Hispanic speakers but it maintains what must be the same in Cuba, Mexico, Chile, Puerto Rico, Spain and in every Spanish speaking country so that each country doesn't loose track of what's Spanish and what's a localism; and it also documents the REALITY of Hispanic speakers :D
I hope all if you may use it as smart Spanish speakers use it :)
Generally speaking, it's a good resource, and I use it like in 99% of the cases when I have a doubt. But anyway, I don't think it should be taken as the only reference, since it has some mistakes. For examples, it says that words such as "guión" mustn't be stressed, but it must.
Well I searched the correct place in the website and it only says the following: (http://lema.rae.es/dpd/?key=gui%C3%B3n) (English) guion o guión: 'Escrito que sirve de guía’ y ‘signo ortográfico’. La doble grafía, con o sin tilde, responde a las dos formas posibles de articular esta palabra: con diptongo (guion [gión]), caso en que es monosílaba y debe escribirse sin tilde; o con hiato (guión [gi - ón]), caso en que es bisílaba y se tilda por ser aguda acabada en -n. La articulación con diptongo es la normal en amplias zonas de Hispanoamérica, especialmente en México y en el área centroamericana; por el contrario, en otros países americanos, como la Argentina, el Ecuador, Colombia y Venezuela, al igual que en España, esta palabra se articula con hiato y resulta, pues, bisílaba. Debido a esta doble articulación, y con el objetivo de preservar la unidad ortográfica, en la última edición de la Ortografía académica (1999) se establece que toda combinación de vocal cerrada átona y abierta tónica se considere diptongo a efectos de acentuación gráfica. Por ello, en guion y otras palabras en la misma situación, como ion, muon, pion, prion, Ruan, Sion y truhan, se da preferencia a la grafía sin tilde, aunque se permite que aquellos hablantes que pronuncien estas voces en dos sílabas puedan seguir tildándolas
(Translation) 'A scripture that serves as a guide' and 'an orthographic symbol'. The double graphic style, with or without an accent mark, responds to the two possible ways to articulate this word: as a diphthong (guion [gión]), the case in which it's a monosyllable and it should be written without an accent mark; or with an hiatus (guión [gi - ón]), the case in which it's a disyllable and it's accented for being acute ending in -n. The articulation with diphthong es the normal way in large zones of Hispanoamerica, specially in Mexico and in the central American area; on the contrary, in other countries, like Argentine, Ecuador, Colombia and Venezuela, the same way as in Spain, this word is articulated with an hiatus and it results, for this reason, disyllable. Because of this double articulation, and with the objective of preserving the orthographic unity, in the last edition of the Academic Orthography (1999) it's stated that every combination of a close atone vowel and an open tonic one is considered as a diphthong in effects of the graphic accent mark. For that, in guion and other words en the same situation like ion, muon, pion, prion, Ruan, Sion y truhan, it's preferable the graphic style without an accent mark, even though it's permitted that those speakers that pronounce these voices in two syllables can continue to accent them. (translated by myself a native Hispanic speaker)
It accepts both pronunciations, it only prefers the pronunciation and the graphic style without a stressed syllable and an accent mark respectively because it's the way MOST OF HISPANOAMERICA, hence the world of Spanish speakers, says it (the way an American should speak Spanish is the way Hispanicamerica speaks it, because it's corresponding to the geographical location of the speaker). It doesn't restrain or say that it's only right in one manner or the other, it only prefers one way with the purpose of maintaining the unity of the language (because again, the majority says it that way), but it accepts both.
I hope this clears out the misunderstanding :) because this is the truth.
I had read kind of a shortened version where it said that it shouldn't be accepted. I hadn't read it all. Sorry.
No worries, that's why I posted it translated :D but trust me, it's the most reliably resource. If you want to talk Spanish you've gotta read from the Royal Spanish Academy, it says all the modern uses in the language :D
Yeah, I know. I used to have the app, but I didn't have enough memory in my phone. I do speak Spanish, is my native language, but I enter there when I have doubts.
Most of Spaniard philologist rarely agree the Academy, although it's true that its web is useful and simple to use... But, please, don't write "cederrón" instead of CD-ROM, as they suggest!