Allow developers to add their own functions to the list of available functions in the RadExpressionEditor and then pass these functions to the LINQ runtime when the expression tree is built. Add support for custom Categories as well.

Scheduled for: 
The feature will be available in R1 2019, scheduled for the mid of January 2019. 

Make it possible to use the expression parser functionality without a reference to the ExpressionEditor control.

When creating an expression that has a decimal, if it doesn't have a zero in front of the decimal, it doesn't evaluate the expression:
eg:  0.02 is valid , .02 is invalid

Allow the string representation of editors to be customized e.g. change the NotEqual operator from "<>" to "!=".

Highlighting logic is not executed correctly when after an invalid expression, another invalid expression is entered.

Incorrect order of operations when brackets are used.

Write 4*(3*2) + 1 in the code editor 

observed result: in the result preview the result is 28

expected result: the result should be 25

Workaround is to add brackets on every operation:
 (4*(3*2)) + 1

Scheduled for: 
The feature will be available in R1 2019, scheduled for the mid of January 2019. 

Respect DisplayNameAttribute of the added fields from fields list in ExpressionTextBox.

The following exception is thrown when translating an expression with a nested member passed to a generic method call:

ArgumentException: 'Value' is not a member of type ' VesselInformation.VesselEventType'

Edit: ExpressionChanged event stops firing in R3 2021 which is a related regression that should be addressed.

The control's template is missing because the Telerik.Windows.Controls.Expressions.xaml file is almost empty. IT misses all RadExpressionEditor related styles and templates. This is valid only for the .xaml file coming from the "Telerik.Windows.Themes.Windows.11.dll" or the "/Telerik UI for WPF installation folder/Themes.Implicit/NetCore/Themes/Windows11/" folder.

Surrounding a string property with double quotation marks by placing the first one at the end of the new value and the second one at the beginning raises a NullReferenceException.

Currently, the RadExpressionEditor control shows a wavy underline and a red color to indicate that an error is present.

We could introduce API to modify this behavior, which will ultimately be used by the ChangeUnderlineDecoration and ChangeUnderlinesColor methods of the internal RadRichTextBox control.

When one clicks on the IF operator in the tree view of the editor the text that should be inserted in the text editor is "IF()". Currently, the text that is being inserted is "Condition()" which cannot be parsed.

A NullReferenceException is thrown when setting the ExpressionText to null.