Add MONTH function description

docs/src/features/serial-numbers.md

@@ -30,4 +30,4 @@ The fractional part of a serial number represents time, as a fraction of the day
 
 Since date-times are stored as numbers, they can be used for arithmetic operations in formulas. For example, it is possible to determine the difference between two dates by subtracting one serial number from the other.
 
-**Note**: A #VALUE! error is reported if a date-formatted cell contains a number less than 1 or greater than 2,958,465.
+**Note**: A #VALUE! error is reported if a date-formatted cell contains a number less than 1, or greater than or equal to 2,958,466.

docs/src/functions/date-and-time.md

@@ -22,7 +22,7 @@ You can track the progress in this [GitHub issue](https://github.com/ironcalc/Ir
 | HOUR             | <Badge type="info" text="Not implemented yet" /> | –             |
 | ISOWEEKNUM       | <Badge type="info" text="Not implemented yet" /> | –             |
 | MINUTE           | <Badge type="info" text="Not implemented yet" /> | –             |
-| MONTH            | <Badge type="tip" text="Available" />          | –             |
+| MONTH            | <Badge type="tip" text="Available" />          | [MONTH](date_and_time/month) |
 | NETWORKDAYS      | <Badge type="info" text="Not implemented yet" /> | –             |
 | NETWORKDAYS.INTL | <Badge type="info" text="Not implemented yet" /> | –             |
 | NOW              | <Badge type="tip" text="Available" />          | –             |

docs/src/functions/date_and_time/month.md

@@ -3,9 +3,35 @@ layout: doc
 outline: deep
 lang: en-US
 ---
-
-# MONTH
-
+# MONTH function
 ::: warning
-🚧 This function is implemented but currently lacks detailed documentation. For guidance, you may refer to the equivalent functionality in [Microsoft Excel documentation](https://support.microsoft.com/en-us/office/excel-functions-by-category-5f91f4e9-7b42-46d2-9bd1-63f26a86c0eb).
+**Note:** This draft page is under construction 🚧
 :::
+## Overview
+MONTH is a function of the Date and Time category that extracts the month from a valid date [serial number](/features/serial-numbers.md), returning a number in the range [1, 12].
+## Usage
+### Syntax
+**MONTH(<span title="Number" style="color:#1E88E5">date</span>) => <span title="Number" style="color:#1E88E5">month</span>**
+### Argument descriptions
+* *date* ([number](/features/value-types#numbers), required). The date for which the month is to be calculated, expressed as a [serial number](/features/serial-numbers.md) in the range [1, 2958466). The value 1 corresponds to the date 1899-12-31, while 2958465 corresponds to 9999-12-31.
+### Additional guidance
+If the supplied _date_ argument has a fractional part, MONTH uses its [floor value](https://en.wikipedia.org/wiki/Floor_and_ceiling_functions).
+### Returned value
+MONTH returns an integer [number](/features/value-types#numbers) in the range [1, 12], that is the month according to the [Gregorian calendar](https://en.wikipedia.org/wiki/Gregorian_calendar). The value 1 corresponds to January, 2 corresponds to February and so on.
+### Error conditions
+* In common with many other IronCalc functions, MONTH propagates errors that are found in its argument.
+* If no argument, or more than one argument, is supplied, then MONTH returns the [`#ERROR!`](/features/error-types.md#error) error.
+* If the value of the *date* argument is not (or cannot be converted to) a [number](/features/value-types#numbers), then MONTH returns the [`#VALUE!`](/features/error-types.md#value) error.
+* For some argument values, MONTH may return the [`#DIV/0!`](/features/error-types.md#div-0) error.
+* If date is less than 0, or greater than or equal to 2,958,466, then MONTH returns the [`#NUM!`](/features/error-types.md#num) error.
+* At present, MONTH does not accept a string representation of a date literal as an argument. For example, the formula `=MONTH("2024-12-31")` returns the [`#VALUE!`](/features/error-types.md#value) error.
+<!--@include: ../markdown-snippets/error-type-details.txt-->
+## Details
+IronCalc utilizes Rust's [chrono](https://docs.rs/chrono/latest/chrono/) crate to implement the MONTH function.
+## Examples
+[See some examples in IronCalc](https://app.ironcalc.com/?example=month).
+
+## Links
+* See also IronCalc's [DAY](/functions/date_and_time/day.md) and [YEAR](/functions/date_and_time/year.md) functions.
+* Visit Microsoft Excel's [MONTH function](https://support.microsoft.com/en-gb/office/month-function-579a2881-199b-48b2-ab90-ddba0eba86e8) page.
+* Both [Google Sheets](https://support.google.com/docs/answer/3093052) and [LibreOffice Calc](https://wiki.documentfoundation.org/Documentation/Calc_Functions/MONTH) provide versions of the MONTH function.