[lmi] Conversion from class html::text

[Greg Chicares]

Vadim--Consider the following inline comment on class text in 'html.hpp':

/// As it still needs to be converted to a string sooner or later to be really
/// used, it does provide a conversion -- but it can be used only once.

What function provides that conversion? I'm guessing it's not this one:
    std::string const& as_html() const&
because I imagine that a const function can be used more than once;
so is it this one:
    std::string&& as_html() &&
?