Editing Pinyin (section)

=== Placement and omission ===
Briefly, tone marks should always be placed in the order {{tlit|zh|a, e, o, i, u, ü}}, with the only exception being {{tlit|zh|iu}} where the tone mark is placed on the second vowel instead. Pinyin tone marks appear primarily above the syllable nucleus—e.g. as in {{tlit|zh|kuài}}, where ''k'' is the initial, ''u'' the medial, ''a'' the nucleus, and ''i'' is the coda. There is an exception for syllabic nasals like {{IPA|/m/}}, where the nucleus of the syllable is a consonant: there, the diacritic will be carried by a written dummy vowel.

When the nucleus is {{IPAslink|ə}} (written ''e'' or ''o''), and there is both a medial and a coda, the nucleus may be dropped from writing. In this case, when the coda is a consonant ''n'' or ''ng'', the only vowel left is the medial ''i, u'', or ''ü'', and so this takes the diacritic. However, when the coda is a vowel, it is the coda rather than the medial which takes the diacritic in the absence of a written nucleus. This occurs with syllables ending in {{tlit|zh|-ui}} (from {{tlit|zh|wei}}: {{tlit|zh|wèi}} → {{tlit|zh|-uì}}) and in {{tlit|zh|-iu}} (from {{tlit|zh|you}}: {{tlit|zh|yòu}} → {{tlit|zh|-iù}}). That is, in the absence of a written nucleus the finals have priority for receiving the tone marker, as long as they are vowels; if not, the medial takes the diacritic.

An algorithm to find the correct vowel letter (when there is more than one) is as follows:
# If there is an ''a'' or an ''e'', it will take the tone mark
# In the combination {{tlit|zh|ou}}, then the ''o'' takes the tone mark
# Otherwise, the second vowel takes the tone mark

Worded differently,
# If there is an ''a, e'', or ''o'', it will take the tone mark; in the case of {{tlit|zh|ao}}, the mark goes on the ''a''
# Otherwise, the vowels are {{tlit|zh|-iu}} or {{tlit|zh|-ui}}, in which case the second vowel takes the tone mark

The above can be summarized as the following table. The vowel letter taking the tone mark is indicated by the fourth-tone mark.
{| class="wikitable" style="text-align:center;border:none"
|+ {{nwr|Placement of the pinyin tone mark}}
! style="background:none;border-style:none" | 
! style="min-width:3em" scope="col" | -a
! style="min-width:3em" scope="col" | -e
! style="min-width:3em" scope="col" | -o
! style="min-width:3em" scope="col" | -i
! style="min-width:3em" scope="col" | -u
|-
! style="min-width:3em" scope="row" | a-
| colspan="2" rowspan="3" class="table-na" style="background-color:#ececec;border-style:none solid none none" | || {{tlit|zh|i=n|ào}}
| {{tlit|zh|i=n|ài}} 
| class="table-na" style="background-color:#ececec;border-style:none solid none none" |
|-
! style="min-width:3em" scope="row" | e-
| rowspan="2" class="table-na" style="background-color:#ececec;border-style:none solid none none" |
| colspan="2" class="table-na" style="background-color:#ececec;border-style:none solid none none"|
|-
! style="min-width:3em" scope="row" | o-
|èi
| {{tlit|zh|i=n|òu}}
|-
! style="min-width:3em" scope="row" | i-
| {{tlit|zh|i=n|ià}}, {{tlit|zh|i=n|iào}}|| {{tlit|zh|i=n|iè}} || {{tlit|zh|i=n|iò}} || class="table-na" style="background-color:#ececec;border-style:none" | || {{tlit|zh|i=n|iù}}
|-
! style="min-width:3em" scope="row" | u-
| {{tlit|zh|i=n|uà}}, {{tlit|zh|i=n|uài}} || {{tlit|zh|i=n|uè}} || {{tlit|zh|i=n|uò}}|| {{tlit|zh|i=n|uì}} 
| class="table-na" style="background-color:#ececec;border-style:none solid none none" | 
|-
! style="min-width:3em" scope="row" | ü-
| {{tlit|zh|i=n|(üà)}} || {{tlit|zh|i=n|üè}}
| colspan="3" |
|}