Currently, when filling out the field for the 'StringFormat' of a Binding, two separate issues can present themselves:

• The inclusion of any ',' (comma) characters generates a XAML error

• StringFormats including a leading pair of '{}' (Curly Braces) has these '{}' characters written to the XAML, but escaped from the Property's field in Studio.

Repro Steps:

1) Create a Studio Project featuring a MainPage.xaml.

2) Introduce 2 TextBlock Elements to the Page, set one to be Left-Aligned+Centre-Aligned, and one Right-Aligned+Centre-Aligned to the Page. It can also be beneficial at this point to increase the Font Size of both TextBlocks.

3) Select one of the TextBlocks, and in the Navigator, rename it to 'Source_TextBlock', then, in its 'Text' Property, input the number '123000'.

4) Select the other TextBlock, hover over its 'Text' Property, and from its 3-Dot Menu, select 'Create Binidng'.

5) Create a Binding for it set to Binding Type: by 'Name', ElementName:'Source_TextBlock', Path 'Text'.

At this point, the TextBlock with the Binding should reflect the Number of the Source_TextBlock TextBlock.

6) Open the Expander under the Binding to reveal the 'StringFormat' Property, and in the 'String Format' Property value, input '#,##0'.

Observe how the number on-screen correctly renders the number '123,000', but produces a XAML error.
Observe the XAML error in VSCode if desired.

7) In the 'StringFormat' Property, instead input '{}{0:#,##0}'

Observe how when pasting the value in, the '{}' leading Curly Braces are escaped.

8) Save all open documents, open the MainPage.xaml in VSCode, and find the StringProperty from Step 7)

Observe how the '{}' Curly Braces are present in code as pasted, but not displayed in Studio.

Expected Results: Commas are supported as part of a StringFormat.
Expected Results: Leading Curly Braces set in the StringFormat value are displayed in Studio.