Are 'elements' defined as non-suffering? I'd like to question something from this answer without disputing it, i.e.  there was a phrase it in which I found novel:


  You do this by seeing that your suffering is impermanent and empty (entirely made up of non-suffering elements i.e. made of the joy of your relationship).


Is it generally true that the "elements" of something are non-suffering?

Is this a well-known, implicit part of (or a reason for) the doctrine of emptiness?

Is this part of the meaning of "sabbe saṅkhārā dukkhā", i.e. it's that combinations of elements, or compounded things, are dukkhā ... but that elements are not?

Is it difficult to identify what's meant by an "element"? The quoted phrase (the "non-suffering elements of a relationship") seems to me to have colloquial meaning, which might be neither an Abhidhamma-like single-moment-in-time or thought-element, nor the "earth, fire, wind, etc." type of classification of element. Can you summarize how to recognize what's an "element"? Do you aim to perceive elements rather than saṅkhārās, and how do you know when/whether you're succeeding? 



I added the mahayana tag because I think the quote is from a Mahayana tradition, but other perspectives would be welcome too.
MN 115 is a comprehensive discourse on elements (dhatu). 

In reality, none of the many elements described in MN 115 are intrinsically 'suffering' because they, as mere elements, are not yet mixed with attachment (upadana). 

Thus, MN 115 states: 


  When, Ānanda, a bhikkhu is skilled in the elements... in that way he can be called a wise man and an inquirer.


The 1st noble truth summarises all suffering as 'attachment' (upadana) and the 2nd noble truth explains the various cravings (tanha) do not give rise (samudhaya) to suffering (dukkha) unless craving creates new becoming (bhava), which is simply more solidified attachment (upadana). 

To quote the 2nd noble truth from SN 56.11: 


  And this, monks, is the noble truth of the origination of stress: the craving that makes for further becoming — accompanied by passion &amp; delight, relishing now here &amp; now there — i.e., craving for
  sensual pleasure, craving for becoming, craving for non-becoming.


The teaching of the 'elements' ('dhatu') is the same as 'sunnata' ('emptiness') therefore any clear discernment of 'elements' quenches suffering because 'elements' are discerned rather than 'self'. 

Again, to quote, this time from MN 62: 


  Rahula... there are these five elements, Rahula. Which five? The earth element, the water element, the fire element, the wind element
  &amp; the space element... Now both the internal elements &amp; the external
  elements are simply elements. And that should be seen as it actually
  is present with right discernment: 'This is not mine, this is not me,
  this is not my self.' When one sees it thus as it actually is present
  with right discernment, one becomes disenchanted with the elements 
  and makes craving for the elements fade from the mind.






The phrase: "sabbe saṅkhārā dukkhā" is unrelated to this answer posted in the question because the word 'dukkhā' in this phrase does not mean 'suffering'. Instead, it means 'unsatisfactoriness', i.e., the incapacity of saṅkhārā (impermanent conditioned things) to bring lasting true happiness. 

This is clearly explained, also in MN 115, as follows: 


  Here, Ānanda, a bhikkhu understands: ‘It is impossible, it cannot happen that a person possessing right view could treat any formation
  as permanent ― there is no such possibility.’ And he understands: ‘It
  is possible that an ordinary person might treat some formation as
  permanent ― there is such a possibility.’ He understands: ‘It is
  impossible, it cannot happen that a person possessing right view could
  treat any formation as pleasurable ― there is no such possibility.’
  And he understands: ‘It is possible that an ordinary person might
  treat some formation as pleasurable ― there is such a possibility.’ He
  understands: ‘It is impossible, it cannot happen that a person
  possessing right view could treat anything as self ― there is no such
  possibility.’ And he understands: ‘It is possible that an ordinary
  person might treat something as self ― there is such a possibility.’


Therefore for example, inanimate objects, such as rocks, trees or stars in the sky, are 'unsatisfactory'; they cannot bring or be relied on for true pleasure; but they are not 'suffering'. 

To avoid doubt, Dhammapada 278 explains the experience of "sabbe saṅkhārā dukkhā" results in liberation rather than suffering: 


  "All conditioned things are unsatisfactory" — when one sees this with wisdom, one turns away from suffering. This is the path to
  purification.
  
  Dhammapada 278