7. The description text will be formatted and justified (right and left edges) to fit between the margins. When the maximum length is reached, the text will be clipped and terminated with an ellipsis. The font is variable pitch, so the maximum number of characters is dependent on the text. The spacing is approximately 85 characters per line x 4 lines = 340 characters. The fonts and character spacing for HD and SD are similar, and display approximately the same number of characters, but the relationship is not exactly 1:1.
Coding from 2010 is so old and is no longer used by Roku. If you are reading this post, you should take it with a grain of salt.
You can find this answer in github's scenegraph coding. Open up any example, then click on components. Look for DetailsScreen or RoScreen or the like.
Did you find it? Now go to the XML below the BRS doc. Open it. You can use this, just take it and change it around so that yours fits in.
I'm always taking pre-existing codes. Remember not to use anything from around 2017 or older, those are mostly being phased out as BrightScript and others are taking over.