Spec: Enhanced Text Trimming

[robloo]

Spec for Enhanced Text Trimming with Prefix Ellipse

Extracted from the PR: #7322. The initial idea isn't my own; however, I wanted to make sure this was more widely seen and reviewed. It would be nice to get in the habit of publicly debating features such as this as is usually done in the WinUI repository.

Overview

Fundamentally, there are a few different generalized concepts:

• BreakMode : By 'Word' or 'Character'
• EllipsisLocation : Start (new), End
  • Note that Middle is not required as the PrefixLength/SuffixLength imply this instead
• PrefixLength/SuffixLength or Length (new)
  • PrefixLength/SuffixLength can be the same property as the start/end information is provided separately (not sure a good name though)
  • Specifying a length will position the ellipsis in the middle of the text

This all could and probably should be calculated using a single generalized method which would support:

Break	Location	Example
Word	End	"first second ..."	Length=0
Word	Start	"... second third"	Length=0
Word	Start	"first... third"	Length=1
Character	End	"first second th..."	Length=0
Character	End	"first seco...hird"	Length=4
Character	Start	"...st second third"	Length=0
Character	Start	"firs...cond third"	Length=4

• Character break mode supports a configurable PrefixLength as specified above but should be extended to support a SuffixLength as well. This would allow ellipsis in the middle that are fully configurable.
• Prefix/SuffixLength can also apply to Word break mode. Fallback logic is as follows:
  • If the length is too long to display, reduce the length to the next integer that fits
  • If even length=1 cannot fit the entire word, switch to using standard character break mode with no length
• Using Prefix/SuffixLength with Word break mode is a bit more complicated to implement and isn't needed in the initial implementation. However, it should be included in the spec so it can be added later.

TextTrimming Enum

Usage in code would involve the following fields:

1. None (default)
2. Clip [Optional] from UWP and CSS spec that trims text by clipping at the pixel level instead of removing characters or words
3. CharacterEllipsis represents BreakMode=Character, EllipsisLocation=End, Length=0
4. WordEllipsis represents BreakMode=Word, EllipsisLocation=End, Length=0
5. PrefixCharacterEllipsis represents BreakMode=Character, EllipsisLocation=Start, Length=0
6. PrefixWordEllipsis represents BreakMode=Word, EllipsisLocation=Start, Length=0

Open Questions:

1. How to make PrefixLength and SuffixLength configurable in XAML. Some special syntax like the nth-child selector may be needed.
2. Rules for right-to-left and symbolic languages (without a distinction between words/characters). Although I can't think of any special cases needed.
3. Defaults for PrefixLength and SuffixLength, strong suggestion is zero for both

References & Links

• CSS spec without a prefix length: https://developer.mozilla.org/en-US/docs/Web/CSS/text-overflow