I'd like to create an expression rule that will set the branding for logo, logo alt text, and/or favicon to either a value specified by expression rule, or (if that is null) the default Appian graphics/alt-text.
Also...if the logo/favicon is saved as a document, is this how you display the correct image?
todocument(<id as provided by expression rule>)
In essence, I want to write the Expression for the branding as something like these lines:
a!defaultValue(todocument(rule!getBranding(attribute: "logoImage")), <Appian's logo's ID>)
a!defaultValue(todocument(rule!getBranding(attribute: "logoAltText")), <Appian's default alt-text for the logo>)
So, basically--if the rule!getBranding with its specified ri!attribute comes up empty, use the Appian defaults for each of logo image, logo alt-text, and favicon.
rule!getBranding
ri!attribute
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You are correct that using todocument with a document ID inside of it will result in a document that be used in the sites designer.
I don't think we have any sort of functions that return the default Appian graphics/alt-text. You may need to download those assets and create documents for them. Then you can easily reference those as constants in your a!defaultValue expression.