Removing/adding rows/columns inside a worksheet requires all the data after them to be translated according to the change. This operation is slow and affects editing performance.

Currently, the chart lines support only solid fill for their outlines.

The API should be able to provide a way to move the X-axis away from the 0 value on the Y-axis or to the bottom of the chart when there are negative Y-axis values.

In Excel this can be achieved by right click on the axis, then from the context menu select "Format Axis".  Go to the "Labels" group and then in the "Label position" field select the desired value.

The COUNTIFS function returns the count of cells that meet one or more criteria.

The data validation rule should have values for formula1 and formula2 elements, which define the start and end values for a range to validate between. When such values are missing, a NullReferenceException is thrown on import and the document cannot be imported.

Details:

Sometimes the customers need to obtain the result of a formula without adding it as a value to a specific cell.

When the worksheet contains many formulas which use large ranges (e.g. covering 50000 cells) as arguments and these formulas have to be calculated, this causes OutOfMemoryException. 

Provide an API used to recalculate all formulas in the document similar to the Excel Interop Calculate function

Exporting empty workbook without any worksheet is not allowed according to the specification and such documents cannot be opened in Excel. Ensure the customers cannot create such documents using the API of SpreadProcessing.

The AlternateContent element is used to store content which is not defined by the specification.

ArgumentException is thrown when importing documents containing empty values

The value formula =Round(1.015, 2) returns 1.01 which is incorrect. Excel returns 1.02.

Add APIs for creating and manipulating Chart objects.

Add support for Point Markes customization options for the Charts.

Add support for Hidden and Empty Cells options:

https://support.office.com/en-us/article/display-empty-cells-null-n-a-values-and-hidden-worksheet-data-in-a-chart-a1ee6f0c-192f-4248-abeb-9ca49cb92274

When a chart is inserted in a document, generated by SpreadProcessing or WordsProcessing, the chart seems to lack any bars. The reason is that some theme information is missing, which effectively makes shapes take their default color, which is transparent. The same applies for shapes inserted in any Document Processing-generated OOXML documents - docx, xlsx.

Workaround: (applicable for Excel) Manually change the theme for the document in MS Excel:
- Choose Page Layout -> Themes -> Themes dropdown -> Office.

ArgumentException with clarification similar to  "'\u001f', hexadecimal value 0x1F, is an invalid character." is thrown when trying to export document containing characters which are not supported in XML document - such as some control characters like 0x00, 0x1F, 0x1B, etc. Such characters are described in the XML specification here: https://www.w3.org/TR/xml/#charsets.

Although the escaped strings are not supported (see  https://feedback.telerik.com/Project/184/Feedback/Details/190228 ), the library could prevent the exception and export the document successfully by skipping such characters.

Workaround: remove such characters before the export. Check the following StackOverflow answer for some ideas on code for replacing the characters: http://stackoverflow.com/a/14323524/259206

Fix available in R3 2018 SP1 release.

Provide the ability to work with images in headers/footers of a worksheet. Note that large images put in headers are visualized as watermarks on printing/exporting to PDF.
Watermark in Excel: https://support.office.com/en-us/article/add-a-watermark-in-excel-a372182a-d733-484e-825c-18ddf3edf009
 

The row declaration is the following:

<row r="8" spans="1:18" ht="15.75" x14ac:dyDescent="0.25">

The dyDescent attribute is described as follows:

The dyDescent attribute is a double attribute, as specified in [XMLSCHEMA2/2] section 3.2.5, that specifies the vertical distance in pixels from the bottom of the cells in the current row to the typographical baseline of the cell content if, hypothetically, the zoom level for the sheet containing this row is 100 percent and the cell has bottom-alignment formatting. See section 2.2.4.12 for how this element integrates with the Office Open XML file formats specified in [ISO/IEC29500-1:2016]. The dyDescent attribute has a side effect; it sets the customHeight attribute to true even if the customHeight attribute is explicitly set to false. 

Note: Since the dyDescent attribute is not implemented, the height is not recognized to be custom and therefore it is not imported at all. The row has the default height.