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Correct .NET Framework bug documentation for MMM format specifier genitive behavior #48061

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adegeo merged 5 commits into from
Sep 23, 2025
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Correct .NET Framework bug documentation for MMM format specifier genitive behavior #48061

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c700953
Initial plan
Copilot Aug 21, 2025
236f06f
Add .NET 8+ version notes for genitive names behavior in MMM and MMMM…
Copilot Aug 21, 2025
9262313
Clarify behavior of 'MMM' and 'MMMM' specifiers in .NET 8
adegeo Aug 21, 2025
a9610a7
Update MMM and MMMM specifier documentation based on feedback
Copilot Aug 25, 2025
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Apply suggestions from code review
adegeo Aug 26, 2025
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Update MMM and MMMM specifier documentation based on feedback 
- Remove version notes from MMMM as it works correctly in both .NET Framework and .NET
- Update MMM to clarify it's a .NET Framework bug that was fixed in .NET

Co-authored-by: adegeo <[email protected]>
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@adegeo
Copilot and adegeo committed Aug 25, 2025
commit a9610a7b1fa5729838afbf9d15fb379b0c8b2397
8 changes: 4 additions & 4 deletions docs/standard/base-types/custom-date-and-time-format-strings.md
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Expand Up @@ -70,8 +70,8 @@ In parsing operations, custom date and time format strings can be used with the
| "mm" | The minute, from 00 to 59.<br /><br /> More information: [The "mm" Custom Format Specifier](#mmSpecifier). | 2009-06-15T01:09:30 -> 09<br /><br /> 2009-06-15T01:45:30 -> 45 |
| "M" | The month, from 1 to 12.<br /><br /> More information: [The "M" Custom Format Specifier](#M_Specifier). | 2009-06-15T13:45:30 -> 6 |
| "MM" | The month, from 01 to 12.<br /><br /> More information: [The "MM" Custom Format Specifier](#MM_Specifier). | 2009-06-15T13:45:30 -> 06 |
| "MMM" | The abbreviated name of the month. When used with "d" or "dd" specifiers, uses genitive names (.NET 8+).<br /><br /> More information: [The "MMM" Custom Format Specifier](#MMM_Specifier). | 2009-06-15T13:45:30 -> Jun (en-US)<br /><br /> 2009-06-15T13:45:30 -> juin (fr-FR)<br /><br /> 2009-06-15T13:45:30 -> Jun (zu-ZA) |
| "MMMM" | The full name of the month. When used with "d" or "dd" specifiers, uses genitive names (.NET 8+).<br /><br /> More information: [The "MMMM" Custom Format Specifier](#MMMM_Specifier). | 2009-06-15T13:45:30 -> June (en-US)<br /><br /> 2009-06-15T13:45:30 -> juni (da-DK)<br /><br /> 2009-06-15T13:45:30 -> uJuni (zu-ZA) |
| "MMM" | The abbreviated name of the month. When used with "d" or "dd" specifiers, uses genitive names (note: this is a known bug in .NET Framework that was fixed in .NET).<br /><br /> More information: [The "MMM" Custom Format Specifier](#MMM_Specifier). | 2009-06-15T13:45:30 -> Jun (en-US)<br /><br /> 2009-06-15T13:45:30 -> juin (fr-FR)<br /><br /> 2009-06-15T13:45:30 -> Jun (zu-ZA) |
| "MMMM" | The full name of the month. When used with "d" or "dd" specifiers, uses genitive names.<br /><br /> More information: [The "MMMM" Custom Format Specifier](#MMMM_Specifier). | 2009-06-15T13:45:30 -> June (en-US)<br /><br /> 2009-06-15T13:45:30 -> juni (da-DK)<br /><br /> 2009-06-15T13:45:30 -> uJuni (zu-ZA) |
| "s" | The second, from 0 to 59.<br /><br /> More information: [The "s" Custom Format Specifier](#sSpecifier). | 2009-06-15T13:45:09 -> 9 |
| "ss" | The second, from 00 to 59.<br /><br /> More information: [The "ss" Custom Format Specifier](#ssSpecifier). | 2009-06-15T13:45:09 -> 09 |
| "t" | The first character of the AM/PM designator.<br /><br /> More information: [The "t" Custom Format Specifier](#tSpecifier). | 2009-06-15T13:45:30 -> P (en-US)<br /><br /> 2009-06-15T13:45:30 -> 午 (ja-JP)<br /><br /> 2009-06-15T13:45:30 -> (fr-FR) |
Expand Down Expand Up @@ -427,7 +427,7 @@ The following example includes the "MM" custom format specifier in a custom form

### <a name="MMM_Specifier"></a> The "MMM" custom format specifier

The "MMM" custom format specifier represents the abbreviated name of the month. The localized abbreviated name of the month is retrieved from the <xref:System.Globalization.DateTimeFormatInfo.AbbreviatedMonthNames%2A?displayProperty=nameWithType> property of the current or specified culture. Starting with .NET 8, if there is a "d" or "dd" custom format specifier in the custom format string, it is retrieved from the <xref:System.Globalization.DateTimeFormatInfo.AbbreviatedMonthGenitiveNames%2A?displayProperty=nameWithType> property instead..
The "MMM" custom format specifier represents the abbreviated name of the month. The localized abbreviated name of the month is retrieved from the <xref:System.Globalization.DateTimeFormatInfo.AbbreviatedMonthNames%2A?displayProperty=nameWithType> property of the current or specified culture. If there is a "d" or "dd" custom format specifier in the custom format string, it is retrieved from the <xref:System.Globalization.DateTimeFormatInfo.AbbreviatedMonthGenitiveNames%2A?displayProperty=nameWithType> property instead. Note that this genitive behavior for "MMM" is a known bug in .NET Framework that was fixed in .NET.

The following example includes the "MMM" custom format specifier in a custom format string.

Expand All @@ -438,7 +438,7 @@ The following example includes the "MMM" custom format specifier in a custom for

### <a name="MMMM_Specifier"></a> The "MMMM" custom format specifier

The "MMMM" custom format specifier represents the full name of the month. The localized name of the month is retrieved from the <xref:System.Globalization.DateTimeFormatInfo.MonthNames%2A?displayProperty=nameWithType> property of the current or specified culture. Starting with .NET 8, if there is a "d" or "dd" custom format specifier in the custom format string, it is retrieved from the <xref:System.Globalization.DateTimeFormatInfo.MonthGenitiveNames%2A?displayProperty=nameWithType> property instead.
The "MMMM" custom format specifier represents the full name of the month. The localized name of the month is retrieved from the <xref:System.Globalization.DateTimeFormatInfo.MonthNames%2A?displayProperty=nameWithType> property of the current or specified culture. If there is a "d" or "dd" custom format specifier in the custom format string, it is retrieved from the <xref:System.Globalization.DateTimeFormatInfo.MonthGenitiveNames%2A?displayProperty=nameWithType> property instead.

The following example includes the "MMMM" custom format specifier in a custom format string.

Expand Down