It's a lot of bloat to stick the entire poem source in the data-mw. It'd be nice if we could edit and serialize from html
An example from
https://incubator.wikimedia.org/w/index.php?title=Wp/grc/%E1%BC%9C%CF%83%CF%84%CE%B7_%CE%9C%CE%AE%CF%84%CE%B7%CF%81&useparsoid=1
<div lang="la" class="poem" typeof="mw:Extension/poem" about="#mwt8" id="mwJQ" data-mw="{"name":"poem","attrs":{"lang":"la"},"body":{"extsrc":"\nStabat mater dolorosa,\njuxta crucem lacrimosa,\n dum pendebat filius.\n\nCujus animam gementem,\ncontristatam et dolentem,\n pertransivit gladius.\n\nO quam tristis et afflicta,\nfuit illa benedicta\n mater unigeniti!\n \nQua moerebat et dolebat,\npia mater, dum videbat\n nati poenas inclyti.\n\nQuis est homo qui non fleret,\nChristi matrem si videret\n in tanto supplicio?\n \nQuis non posset contristari\npiam matrem contemplari\n dolentem cum filio?\n\nPro peccatis suae gentis,\nvidit Jesum in tormentis,\n et flagellis subditum.\n \nVidit suum dulcem natum,\nmorientem, desolatum,\n dum emisit spiritum.\n\nEia mater, fons amoris,\nme sentire vim doloris\n fac, ut tecum lugeam.\n \nFac ut ardeat cor meum,\nin amando Christum Deum\n ut illi complaceam.\n\nSancta Mater, istud agas,\nCrucifixi fige plagas\n cordi meo valide.\n \nTui Nati vulnerati,\ntam dignati pro me pati,\n poenas mecum divide.\n\nFac me vere tecum flere,\ncrucifixo condolere,\n donec ego vixero.\n \nJuxta crucem tecum stare,\net tibi me sociare\n in planctu desidero.\n\nVirgo virginum praeclara,\nmihi jam non sis amara;\n fac me tecum plangere.\n \nFac ut portem Christi mortem\npassionis fac consortem,\n et plagas recolere.\n\nFac me plagis vulnerari,\naac me cruce inebriari,\n et cruore filii.\n \nInflammatus et accensus,\nper te, Virgo, sim defensus,\n in die judicii.\n\nFac me cruce custodiri,\nmorte Christi praemuniri,\n confoveri gratia.\n \nQuando corpus morietur,\nfac ut animae donetur\n paradisi gloria.\n"}}"><p id="mwJg">Stabat mater dolorosa,<br id="mwJw">
juxta crucem lacrimosa,<br id="mwKA">
<span typeof="mw:Entity" id="mwKQ"> </span> dum pendebat filius.<br id="mwKg">
<br id="mwKw">
Cujus animam gementem,<br id="mwLA">
contristatam et dolentem,<br id="mwLQ">
<span typeof="mw:Entity" id="mwLg"> </span> pertransivit gladius.<br id="mwLw">
<br id="mwMA">
O quam tristis et afflicta,<br id="mwMQ">
fuit illa benedicta<br id="mwMg">
<span typeof="mw:Entity" id="mwMw"> </span> mater unigeniti!<br id="mwNA">
<span typeof="mw:Entity" id="mwNQ"> </span><br id="mwNg">
Qua moerebat et dolebat,<br id="mwNw">
pia mater, dum videbat<br id="mwOA">
<span typeof="mw:Entity" id="mwOQ"> </span> nati poenas inclyti.<br id="mwOg">
<br id="mwOw">
Quis est homo qui non fleret,<br id="mwPA">
Christi matrem si videret<br id="mwPQ">
<span typeof="mw:Entity" id="mwPg"> </span> in tanto supplicio?<br id="mwPw">
<span typeof="mw:Entity" id="mwQA"> </span><br id="mwQQ">
Quis non posset contristari<br id="mwQg">
piam matrem contemplari<br id="mwQw">
<span typeof="mw:Entity" id="mwRA"> </span> dolentem cum filio?<br id="mwRQ">
<br id="mwRg">
Pro peccatis suae gentis,<br id="mwRw">
vidit Jesum in tormentis,<br id="mwSA">
<span typeof="mw:Entity" id="mwSQ"> </span> et flagellis subditum.<br id="mwSg">
<span typeof="mw:Entity" id="mwSw"> </span><br id="mwTA">
Vidit suum dulcem natum,<br id="mwTQ">
morientem, desolatum,<br id="mwTg">
<span typeof="mw:Entity" id="mwTw"> </span> dum emisit spiritum.<br id="mwUA">
<br id="mwUQ">
Eia mater, fons amoris,<br id="mwUg">
me sentire vim doloris<br id="mwUw">
<span typeof="mw:Entity" id="mwVA"> </span> fac, ut tecum lugeam.<br id="mwVQ">
<span typeof="mw:Entity" id="mwVg"> </span><br id="mwVw">
Fac ut ardeat cor meum,<br id="mwWA">
in amando Christum Deum<br id="mwWQ">
<span typeof="mw:Entity" id="mwWg"> </span> ut illi complaceam.<br id="mwWw">
<br id="mwXA">
Sancta Mater, istud agas,<br id="mwXQ">
Crucifixi fige plagas<br id="mwXg">
<span typeof="mw:Entity" id="mwXw"> </span> cordi meo valide.<br id="mwYA">
<span typeof="mw:Entity" id="mwYQ"> </span><br id="mwYg">
Tui Nati vulnerati,<br id="mwYw">
tam dignati pro me pati,<br id="mwZA">
<span typeof="mw:Entity" id="mwZQ"> </span> poenas mecum divide.<br id="mwZg">
<br id="mwZw">
Fac me vere tecum flere,<br id="mwaA">
crucifixo condolere,<br id="mwaQ">
<span typeof="mw:Entity" id="mwag"> </span> donec ego vixero.<br id="mwaw">
<span typeof="mw:Entity" id="mwbA"> </span><br id="mwbQ">
Juxta crucem tecum stare,<br id="mwbg">
et tibi me sociare<br id="mwbw">
<span typeof="mw:Entity" id="mwcA"> </span> in planctu desidero.<br id="mwcQ">
<br id="mwcg">
Virgo virginum praeclara,<br id="mwcw">
mihi jam non sis amara;<br id="mwdA">
<span typeof="mw:Entity" id="mwdQ"> </span> fac me tecum plangere.<br id="mwdg">
<span typeof="mw:Entity" id="mwdw"> </span><br id="mweA">
Fac ut portem Christi mortem<br id="mweQ">
passionis fac consortem,<br id="mweg">
<span typeof="mw:Entity" id="mwew"> </span> et plagas recolere.<br id="mwfA">
<br id="mwfQ">
Fac me plagis vulnerari,<br id="mwfg">
aac me cruce inebriari,<br id="mwfw">
<span typeof="mw:Entity" id="mwgA"> </span> et cruore filii.<br id="mwgQ">
<span typeof="mw:Entity" id="mwgg"> </span><br id="mwgw">
Inflammatus et accensus,<br id="mwhA">
per te, Virgo, sim defensus,<br id="mwhQ">
<span typeof="mw:Entity" id="mwhg"> </span> in die judicii.<br id="mwhw">
<br id="mwiA">
Fac me cruce custodiri,<br id="mwiQ">
morte Christi praemuniri,<br id="mwig">
<span typeof="mw:Entity" id="mwiw"> </span> confoveri gratia.<br id="mwjA">
<span typeof="mw:Entity" id="mwjQ"> </span><br id="mwjg">
Quando corpus morietur,<br id="mwjw">
fac ut animae donetur<br id="mwkA">
<span typeof="mw:Entity" id="mwkQ"> </span> paradisi gloria.</p></div>