HTML constructor should only accept AbstractString #38540
Description
The Base.HTML datatype seems an ideal wrapper to indicate that a given string object is suitable for direct presentation to a browser. However, currently the HTML type's constructor accepts any sort of object for its argument and does not use the object's text/html representation.
function HTML(xs...)
HTML() do io
for x in xs
print(io, x)
end
end
end
By printing, without providing the text/html mimetype, the HTML constructor is not using the hypertext representation of an object, as one would expect. Indeed, it doesn't even handle nesting of itself in a reasonable way.
julia> fragment = html"<span>Hello!</span>"
HTML{String}("<span>Hello!</span>")
julia> display("text/html", fragment)
<span>Hello!</span>
julia> display("text/html", HTML(fragment))
HTML{String}("<span>Hello!</span>")
This inability to handle itself (or other objects with hypertext rendering) poses a challenge when trying to use HTML as a unit of composition between various libraries and components that produce HTML.
A conservative option is to limit the HTML constructor to only AbstractString.
Long term, a coherent design rationale for this datatype and supporting operations could be worked out and implemented. For example, join could be made to accept an array of HTML objects and providing an HTML output of the concatenated content strings.
As more and more applications of Julia involve deep interactions with a web browser, having a standardized unit of composition for hypertext fragments would be immensely useful. This ticket could be discussed in a discourse thread.