Use the initial-letter contraction for "under" except when the letters it represents are preceded by the vowels "a" or "o" and when the letters "un" form a prefix.

Use the final-letter groupsign when the letters it represents follow a letter, a contraction, a modified letter or a ligatured letter unless other rules limit its use.

Do not use the final-letter groupsign when the letters it represents follow a capitals indicator or a capitals terminator.

Do not use the final-letter groupsign for "ity" in the words: biscuity, dacoity, fruity, hoity-toity and rabbity.

Do not use the final-letter groupsign for "ness" when the feminine ending "ess" is added to a word ending in "en" or "in".

Use the shortform whenever the word it represents is "standing alone", regardless of meaning or pronunciation, and regardless of whether the word is used as an ordinary word or as a proper name. 

Refer to: Section 2.6, Terminology and General Rules, for the definition of "standing alone".

Use the shortform within a longer word provided that the longer word is "standing alone” (including any affix with an apostrophe) and that the longer word: (a) appears on the Shortforms List given in Appendix 1; or (b) satisfies the provisions of rule 10.9.3.

Note: Rule 10.9.2 encompasses words which are ordinary words, proper names and artificial or contrived words.

Use any of the ten shortforms listed below within a longer word that is not on the Shortforms List, provided the word is "standing alone" (including any affix with an apostrophe) and that any restrictions for the shortform are met.
(a) "braille" or "great": Use the shortform wherever it occurs.
(b) "children": Use the shortform provided that it is not followed by a vowel or "y".
(c) "blind", "first", "friend", "good", "letter", "little" or "quick": Use the shortform if it begins the word and is not followed by a vowel or "y".

Do not use a groupsign that would form part of the shortform.

Use a grade 1 symbol indicator before a letters-sequence that could be read as a shortform when "standing alone", or which occurs at the beginning of a longer letters-sequence.