using GtkHTML and GtkSourceView in a Glade app

[William Page <compenguy gmail com>]

I'm trying to build a Gnome app that has a GtkNotebook with 2 tabs,
one containing a GtkHTML, and one containing a GtkSourceView, but they
just don't show up, and I get an error from glade trying to add the
GtkHTML widget.

glade-2 doesn't have built-in support for those widgets, but it does
have a "Custom" widget.  So I have in my glade project a GtkNotebook
with 2 tabs.  Each tab contains a GtkScrolledWindow, each of which, in
turn, contains a GtkViewport, which contains the glade "Custom"
widget.

Each of the two custom widgets has a creation function:
uihandler_document_html_init
uihandler_html_sourceview_init

With prototypes like:
GtkWidget *uihandler_html_sourceview_init(gchar *name, gchar *str1,
gchar *str2, gint val1, gint val2);
GtkWidget *uihandler_document_html_init(gchar *name, gchar *str1,
gchar *str2, gint val1, gint val2);

and the functions look like:
GtkWidget *uihandler_document_html_init(gchar *name, gchar *str1,
gchar *str2, gint val1, gint val2)
{
    GtkWidget *document_html;

    if(str1)
    {
        document_html = gtk_html_new_from_string(str1, -1);
    }
    else
    {
        document_html = gtk_html_new();
    }
    return document_html;
}

GtkWidget *uihandler_html_sourceview_init(gchar *name, gchar *str1,
gchar *str2, gint val1, gint val2)
{
    GtkSourceBuffer *sourceBuffer;
    GtkSourceLanguagesManager *languagesManager;
    GtkSourceLanguage *language;

    languagesManager = gtk_source_languages_manager_new();
    language = gtk_source_languages_manager_get_language_from_mime_type(languagesManager,
"text/html");
    sourceBuffer = gtk_source_buffer_new_with_language(language);
    if(str1)
    {
        gtk_text_buffer_insert_at_cursor(GTK_TEXT_BUFFER(sourceBuffer),
str1, -1);
    }
    return gtk_source_view_new_with_buffer(sourceBuffer);
}

The program compiles with no warnings or errors, and upon running:
** (eEd:24337): CRITICAL **: html_utils_get_accessible: assertion `o
!= NULL' failed

and both notebook pages come up blank.

Any ideas?
Will Page