Sound changes
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West Saxons conquer bits of Wales in ~700 AD (so before the merger of /iu/ into /eo/), get cut off from the rest of the English speakers, some Welsh influence, generally like Yola.

Begin with Old English. Inventory:

/p b t d tʃ (dʒ) k ɣ/ (writing ɣ as g)
/f θ s/ + voiced allophones
/ʃ h/
/m n/
/l r j w/

/æ a e o i y u/ + length
/ea eo iu ie/ + length (the precise interpretation doesn't really matter)
some diphthongs in -j -w

a:n twa: θriu: feo:wor fi:f siks seovon eahta nijon tie:n

700 - 1300

e o > ɛ ɔ (this was probably already the case)

Diphthong loss:
ea > a / _lC _rC
ea ea: eo eo: > ɛ a: ɛ e: / w_
ea ea: > ɛ ja:
eo eo: > jɔ jo:
io io: > jɔ ju:
ie ie: > ɨ ɨː, sporadic merger of short ie into y esp. around labials

æ æ: æ(:)j > a ɛ: e(:)j
i > 0 / _jV
e: > wɨ:
wɨ: > ɨ: / [+lab]_ [+pal]_
wɨ: > u: / CCC_
tj sj > tʃ ʃ
ɨ > i / [+pal]_
ɔ o: > u ou: / _n(g)
a a: > ɔ ɔ: / _N EXCEPT _NV
a: ɛ: > æ: e:

m > n / _# in unstressed syllables

Length confusion:
V: > V / _C{:,C} ! _st{#,V}
V[+stress] > V: / sP θP nd ld
V[+stress] > V: > _(C)#
trisyllabic laxing
ɛ ɔ > e o

Y loss:
y(:) > e(:) / _(n)g _h _l _r
y(:) > ɨ(:)w / _x(C)#
y: > i:w / {t d s z tʃ ʃ n}_
y(:) > ɨ(:)

æ a e o i ɨ u
æ: a: ɛ: ɔ: e: o: i: ɨ: u:

ɔ:n twa: θrju: fjo:wor fi:f siks ʃovon ɛhta njun tɨ:n

More sound changes:

ɣ loss (NB: Rg nouns > Rv)
ɣ > w > v / _R
ɣ > 0 / #_ (sporadic), #g

ɣ > ə̯ / {l r}_#
ə̯ > v / [+round]+_ in monosyllables (i.e. when the vowel of the preceding syllable was round)
V[-diphthong]+ə̯ > Vj (i.e. ə̯ > j, which then metathesizes onto the end of the vowel of the preceding syllable if said vowel was a monophthong)
ə̯ > 0
ɣ > j / V[+front]_V VC_V[+front]
ɣ > w / V[-front]_V VC_V[-front]

0 > j / V[-front]_+i
jV[-stress] > i / C_
j w > 0 / C_V[-stress]

Glide+vowel simplification:
V(:)vV V(:)wV > V(:)u / _C _#
V(:)jV > V(:)j / _C _#

al ol > au ou / _{C #}

Diphthong simplification:
eu: iu iu: > ɛu: ju ju:
ou: > ɔu:
w > 0 / _u
j > 0 / _i

Yod breaking:
ju(:) > i(:)u / Cr_ CCC_
j > ij / Cr_ CCC_
ijǝ > i:

s > ʃ / _C

a ɛ ɔ > oə eə ɔu / _[+stress]N
oə eə > ɔ i

Disyllabic stress shift: 'CVCV > CV'CV. Sporadic when no final C, universal when final C. Attested more regularly in Yola, which showed (semi?)regular final stress — *after* vowel reduction. Doesn't happen if first C is a cluster or if first vowel is long.
Trisyllabic stress shift from initial to penultimate. Should be fairly regular but this might happen later.

Diphthong loss before r:
au ɔu > ɔ: o: / _r
Vj > Vjə / _r

Vowel reduction:
All short vowels in unstressed syllables > ǝ. All long vowels in unstressed syllables shorten. Diphthongs coalesce; will figure this out if I have to.

Length confusion:
Diphthongs lose contrastive vowel length.
Consonants lose length entirely. Voiceless fricatives now contrast with voiced.

w > 0 / C_V[+back]
v > w / _(C)#
jǝ ǝj > i

Numerals: a:n twa: θriu fjɔur fi:f siks ʃɔun jahtǝ njon tɨːn

[size=150]1600-2013:[/size] (after spelling began to be standardized, although older conventions can, of course, carry over)

Sporadic final loss of grammatical -n.

Yod loss:
j > 0 / V_{ŋ rk rg}
lj > j / C_

F[-voice] > F[+voice] / #_

ɛ ɛ: > i ɛi / _ŋ _[+pal]
ɛ > i / _nC

g > 0 / ŋ_
mb nd > m n n
nt > n / V[-stress]_

w > v / #_C

hw > f (welsh loans with xw should be borrowed as with hw so xw shouldn't occur)
dw kw > b f
hm hn hŋ hr hj > m n ŋ r j (hŋ shouldn't occur ever in the first place)
r > ʃ / _P[-voice]

0 > ə / C_{r l n} {l r}_{m v} ð_v (stolen verbatim from the Welsh rule)

sP > Ps / _# (sporadic, in many cases existing since before the OE-WE split)

TODO: weird length shit like trisyllabic laxing and book-blood; mergers before l and r; more weird metathesis shit; h-dropping; th-dropping as Cardiff?; presumably some eventual English influence