Spanish language Q&A Forum

Que tal,

How interchangeable are tras and detrás? Is one preferred over another, and if so, does it vary by country or age or context?

I'm think about basic use meaning 'behind,' such as "El niño se escondía tras (detrás) las cortinas."

Thanks!

Is it interchangeable to say something like

Just as 'tal vez' and "quizás" are interchangeable, with no fast rules on them, is it the same for using quizá and quizás or is there some guide for when they can/can't be used?

also, is it impossible to use quizá/quizás/tal vez using future tenses? 
examples:

"Quizá iré a la biblioteca pasado mañana"
"Tal vez conocerás aquel varón cuando venga"
"Quizás recibiré una mejor evaluación cuando mejore mis debilidades en mi trabajo"

I have encountered real-life examples using both indicative and subjunctive with "una vez que..." and I'm just hoping to confirm or correct my understanding of how this works, please...? For examples, In an article about animals' senses of smell, in discussing the properties of volatile scent compounds I read "Una vez que se vaporiza, puede extenderse rápidamente por el aire" and in a tutorial for making tortillas mexicanas I found "Una vez que sepas cómo hacer tortillas..." I'm thinking that the first takes the indicative because its describing something factual understood to happen routinely, whereas the second takes the subjunctive because it's referring to something that from the writer's point of view hasn't happened yet or is more a hypothetical idea. Is this an accurate way to understand this or am I missing something...? If this is accurate, does it generally hold true with other, similar constructions like those discussed in this lesson? Thanks in advance, as I appreciate the help!

Are there 2 adverbs cuándo and cuando? WordReference.com has both listed. I need an explanation on this for A1 beginner (me).

In an example above you say, "Ellos estan delgados". I thought SER was used to describe physical characteristics i.e. "El es alto." To say Ellos estan delgados would imply they are thin now but they didn't used to be thin. Or that they appear thin. Or am I wrong?