/
^
# Uncomment to allow prefix continuation (second letter of a dangling match)
# ([abcdefghiklmnoprstuvy\ ])?
( \
|(?: # Single-letter elements
[BCFHIKNOPSUVWY]
)
|(?: # Two-letter elements.
(?:A[cglmrstu])|(?:B[aehikr])|(?:C[adeflmnorsu])|(?:D[bsy])
| (?:E[rsu])|(?:F[elmr])|(?:G[ade])|(?:H[efgos])|(?:I[nr])
| (?:K[r])|(?:L[airuv])|(?:M[cdgnot])|(?:N[abdehiop])
| (?:O[gs])|(?:P[abdmortu])|(?:R[abefghnu])|(?:S[bcegimnr])
| (?:T[abcehilms])|(?:X[e])|(?:Yb)|(?:Z[nr])
)
|(?: # Smushed trigrams. No need to go