richEdit.commands.insertText.execute('sometext');

richEdit.selection.goToDocumentEnd();
richEdit.commands.insertText.execute("sometext");

richEdit.selection.selectAll();
richEdit.commands.delete.execute();

var imageUrl = "https://demos.devexpress.com/ASPxImageAndDataNavigationDemos/Content/Images/landscapes/07.jpg";
richEdit.selection.intervals = [{ start: position, length: 0 }];
richEdit.commands.insertPicture.execute(imageUrl);

var mainSubDocumentLength = richEdit.document.mainSubDocument.length;

var mainSubDocumentText = richEdit.document.mainSubDocument.text;

var firstSelectedInterval = richEdit.selection.intervals[0];
var selectedText = richEdit.document.activeSubDocument.text.substr(firstSelectedInterval.start, firstSelectedInterval.length);

var mainSubDocumentFields = richEdit.document.mainSubDocument.fieldsInfo;

richEdit.commands.createField.execute('time');

richEdit.commands.updateAllFields.execute();

richEdit.commands.insertHeader.execute();
richEdit.commands.insertText.execute("sometext");
richEdit.commands.closeHeaderFooter.execute();

richEdit.selection.intervals = [{ start: tblPosition, length: 0 }];
richEdit.commands.insertTable.execute(2, 3);

richEdit.commands.goToBookmark.execute("bookmarkName");

var bookmarkInterval = richEdit.document.mainSubDocument.findBookmarks('bookmark')[0].interval;

richEdit.scroll.setByDocumentPosition(richEdit.document.mainSubDocument.length);

var fields = richEdit.document.mainSubDocument.fieldsInfo;
var hyperlinkUrls = [];
for(var i = 0; i < fields.length; i++) {
    var field = fields[i];
    if(field.isHyperlink && field.hyperlinkUri)
        hyperlinkUrls.push(field.hyperlinkUri);
}

var selection = richEdit.selection.intervals;
richEdit.selection.setSelection(richEdit.document.mainSubDocument.fieldsInfo[0].interval);
richEdit.commands.delete.execute();
richEdit.selection.intervals = selection;

<dx:ASPxRichEdit ID="richEdit" runat="server" Width="100%" Height="700px">
    <ClientSideEvents DocumentLoaded="function(s, e) {s.commands.updateAllFields.execute();}" />
</dx:ASPxRichEdit>

<script type="text/javascript">
function onContentInserted(s, e) {
    var previousSelection = s.selection.intervals;
    s.commands.beginUpdate();
    s.selection.intervals = [e.interval];
    s.commands.changeFontSize.execute(10);
    s.selection.intervals = previousSelection;
    s.commands.endUpdate();
}
</script>

<dx:ASPxRichEdit ID="richEdit" runat="server" ClientInstanceName="richEdit">
    <ClientSideEvents ContentInserted="OnContentInserted"/>
</dx:ASPxRichEdit>

<dx:ASPxButton runat="server" ID="InsertModel" Text="Insert Model">
    <ClientSideEvents Click="function(s, e) {richEdit.commands.insertContentFromServer.execute('model');}" />
</dx:ASPxButton>
<dx:ASPxRichEdit ID="richEdit" runat="server" ClientInstanceName="richEdit" 
    OnInsertContentToClient="ASPxRichEdit1_InsertContentToClient">
</dx:ASPxRichEdit>

protected void ASPxRichEdit1_InsertContentToClient(object sender, DevExpress.Web.ASPxRichEdit.InsertContentToClientEventArgs e) {
    if (e.RequestId == "model") {
        var docServer = new RichEditDocumentServer();
        var document = docServer.Document;

        document.AppendText("Model To Insert");
        DocumentRange myRange = document.Paragraphs[0].Range;
        CharacterProperties charProps = document.BeginUpdateCharacters(myRange);
        charProps.FontSize = 30;
        charProps.Bold = true;
        document.EndUpdateCharacters(charProps);
        e.Result = document;
    }
}

Protected Sub ASPxRichEdit1_InsertContentToClient(ByVal sender As Object, ByVal e As DevExpress.Web.ASPxRichEdit.InsertContentToClientEventArgs)
    If e.RequestId = "model" Then
        Dim docServer = New RichEditDocumentServer()
        Dim document = docServer.Document
        document.AppendText("Model To Insert")
        Dim myRange As DocumentRange = document.Paragraphs(0).Range
        Dim charProps As CharacterProperties = document.BeginUpdateCharacters(myRange)
        charProps.FontSize = 30
        charProps.Bold = True
        document.EndUpdateCharacters(charProps)
        e.Result = document
    End If
End Sub