The bigrams can be used at the beginnings, middles or endings of words.
Sh cannot be used to indicate a request for silence; it must be spelled out. St can be used as an abbreviation for street or saint. St and th can be used in ordinal symbols like 21st or 8th.
Ed, er and ow can be used as single words (a name, an uncertain sound and an interjection).
These two contractions can appear in the middle of a word, or at the end, but not at the beginning.
While in can be used as a word in Latin phrases, en cannot be used as a word in French phrases.
These prefixes can also be used in a hyphenated word as the first syllable after the hyphen, but not in a syllabized word, even as the first syllable.
These prefixes can follow apostrophes, but not precede them.
Con cannot be used as a word by itself (as in con game) and must be spelled out.
These prefixes can be used in abbreviations if used as a prefix, and if the prefix does not constitute the entire abbreviation.
Com cannot contact a hyphen, dash, or apostrophe.
Com can also be used in abbreviations as long as it's not the entire abbreviation.