A possible workaround: 
	<form id="form1" runat="server">
		<telerik:RadScriptManager ID="RadScriptManager1" runat="server"></telerik:RadScriptManager>
		<script>
			var ExplodeLevel = 0.15;
		</script>
		<telerik:RadHtmlChart runat="server" ID="PieChart1" Transitions="true">
			<PlotArea>
				<Series>
					<telerik:PieSeries StartAngle="90">
						<LabelsAppearance Position="OutsideEnd" DataFormatString="{0} %" />
						<TooltipsAppearance DataFormatString="{0} %" />
						<SeriesItems>
							<telerik:PieSeriesItem BackgroundColor="Purple" Exploded="true" Name="Internet Explorer" Y="18.3" />
							<telerik:PieSeriesItem BackgroundColor="Orange" Exploded="false" Name="Firefox" Y="35.8" />
							<telerik:PieSeriesItem BackgroundColor="Green" Exploded="false" Name="Chrome" Y="38.3" />
							<telerik:PieSeriesItem BackgroundColor="Blue" Exploded="true" Name="Safari" Y="4.5" />
							<telerik:PieSeriesItem BackgroundColor="Red" Exploded="false" Name="Opera" Y="2.3" />
						</SeriesItems>
					</telerik:PieSeries>
				</Series>
			</PlotArea>
			<ChartTitle Text="Browser Usage for April 2012">
			</ChartTitle>
		</telerik:RadHtmlChart>
		<script>
			var math = Math,
				dataviz = kendo.dataviz,
				Box2D = dataviz.Box2D,
				Point2D = dataviz.Point2D,
				OUTSIDE_END = "outsideEnd",
				RIGHT = "right",
				util = kendo.util,
				valueOrDefault = util.valueOrDefault;

			kendo.dataviz.PieChart.fn.reflow = function (targetBox) {
				var chart = this,
					options = chart.options,
					box = targetBox.clone(),
					space = 5,
					minWidth = math.min(box.width(), box.height()),
					halfMinWidth = minWidth / 2,
					defaultPadding = minWidth - minWidth * 0.85,
					padding = valueOrDefault(options.padding, defaultPadding),
					newBox = Box2D(box.x1, box.y1,
					box.x1 + minWidth, box.y1 + minWidth),
					newBoxCenter = newBox.center(),
					seriesConfigs = chart.seriesConfigs || [],
					boxCenter = box.center(),
					points = chart.points,
					count = points.length,
					seriesCount = options.series.length,
					leftSideLabels = [],
					rightSideLabels = [],
					seriesConfig, seriesIndex, label,
					segment, sector, r, i, c;

				padding = padding > halfMinWidth - space ? halfMinWidth - space : padding;
				newBox.translate(boxCenter.x - newBoxCenter.x, boxCenter.y - newBoxCenter.y);
				r = halfMinWidth - padding;
				c = Point2D(
					r + newBox.x1 + padding,
					r + newBox.y1 + padding
				);

				for (i = 0; i < count; i++) {
					segment = points[i];

					sector = segment.sector;
					sector.r = r;
					sector.c = c;
					seriesIndex = segment.seriesIx;
					if (seriesConfigs.length) {
						seriesConfig = seriesConfigs[seriesIndex];
						sector.ir = seriesConfig.ir;
						sector.r = seriesConfig.r;
					}

					if (seriesIndex == seriesCount - 1 && segment.explode) {
						sector.c = sector.clone().radius(sector.r * ExplodeLevel).point(sector.middle());
					}

					segment.reflow(newBox);

					label = segment.label;
					if (label) {
						if (label.options.position === OUTSIDE_END) {
							if (seriesIndex == seriesCount - 1) {
								if (label.orientation === RIGHT) {
									rightSideLabels.push(label);
								} else {
									leftSideLabels.push(label);
								}
							}
						}
					}
				}

				if (leftSideLabels.length > 0) {
					leftSideLabels.sort(chart.labelComparator(true));
					chart.leftLabelsReflow(leftSideLabels);
				}

				if (rightSideLabels.length > 0) {
					rightSideLabels.sort(chart.labelComparator(false));
					chart.rightLabelsReflow(rightSideLabels);
				}

				chart.box = newBox;
			};
		</script>
	</form>

For the time being you can use the following workaround:

        <telerik:RadScriptManager ID="RadScriptManager1" runat="server"></telerik:RadScriptManager>
        <script>
            function pageLoad() {
                var position = 'insideEnd'; // 'center'
                $find("<%=PieChart1.ClientID%>")._chartObject.options.series[0].labels.position = position;
                $find("<%=PieChart1.ClientID%>")._chartObject.options.series[0].labels.distance = -20;
                $find("<%=PieChart1.ClientID%>")._chartObject.redraw();
            }
        </script>
        <telerik:RadHtmlChart runat="server" ID="PieChart1" Transitions="true">
            <PlotArea>
                <Series>
                    <telerik:PieSeries StartAngle="90">
                        <LabelsAppearance DataFormatString="{0} %" />
                        <TooltipsAppearance DataFormatString="{0} %" />
                        <Items>
                            <telerik:SeriesItem BackgroundColor="Purple" Exploded="true" Name="Internet Explorer" YValue="18.3" />
                            <telerik:SeriesItem BackgroundColor="Orange" Exploded="false" Name="Firefox" YValue="35.8" />
                            <telerik:SeriesItem BackgroundColor="Green" Exploded="false" Name="Chrome" YValue="38.3" />
                            <telerik:SeriesItem BackgroundColor="Blue" Exploded="false" Name="Safari" YValue="4.5" />
                            <telerik:SeriesItem BackgroundColor="Red" Exploded="false" Name="Opera" YValue="2.3" />
                        </Items>
                    </telerik:PieSeries>
                </Series>
            </PlotArea>
            <ChartTitle Text="Browser Usage for April 2012">
            </ChartTitle>
        </telerik:RadHtmlChart>
        <script>
            var INSIDE_END = "insideEnd",
                CENTER = "center",
                LEFT = "left",
                RIGHT = "right",
                dataviz = kendo.dataviz,
                Box2D = dataviz.Box2D,
                math = Math;

            kendo.dataviz.PieSegment.fn.reflowLabel = function () {
                var segment = this,
                    sector = segment.sector.clone(),
                    options = segment.options,
                    label = segment.label,
                    labelsOptions = options.labels,
                    labelsDistance = labelsOptions.distance,
                    angle = sector.middle(),
                    lp, x1, labelWidth, labelHeight;

                if (label) {
                    labelHeight = label.box.height();
                    labelWidth = label.box.width();
                    if (labelsOptions.position == CENTER) {
                        sector.r = math.abs((sector.r - labelHeight) / 2) + labelHeight + labelsDistance;
                        lp = sector.point(angle);
                        label.reflow(Box2D(lp.x, lp.y - labelHeight / 2, lp.x, lp.y));
                    } else if (labelsOptions.position == INSIDE_END) {
                        sector.r = sector.r - labelHeight / 2 + labelsDistance;
                        lp = sector.point(angle);
                        label.reflow(Box2D(lp.x, lp.y - labelHeight / 2, lp.x, lp.y));
                    } else {
                        lp = sector.clone().expand(labelsDistance).point(angle);
                        if (lp.x >= sector.c.x) {
                            x1 = lp.x + labelWidth;
                            label.orientation = RIGHT;
                        } else {
                            x1 = lp.x - labelWidth;
                            label.orientation = LEFT;
                        }
                        label.reflow(Box2D(x1, lp.y - labelHeight, lp.x, lp.y));
                    }
                }
            }
        </script>

For the time being you can resize the chart with set_width/set_height methods. For example:

<head runat="server">
	<title></title>
	<style>
		.RadHtmlChart.k-chart, table {
			width: 100%;
			height: 100%;
		}

		td {
			border: 1px solid green;
			width: 60%;
			height: 60%;
			overflow:hidden;
		}

		html, body, form {
			height: 100%;
			overflow: hidden;
			margin: 0;
		}
	</style>
</head>
<body>
	<form id="form1" runat="server">
		<telerik:RadScriptManager ID="RadScriptManager1" runat="server"></telerik:RadScriptManager>
		<script>
			function resizedw() {
				// Haven't resized in 100ms!
				var donut = $find("<%=DonutChart.ClientID%>");
				var radar = $find("<%=RadarAreaChart.ClientID%>");

				var docDimensions = $telerik.getBounds(document.body);
				resizeChart(donut, docDimensions);
				resizeChart(radar, docDimensions);
			}

			function resizeChart(chart, docDimensions) {
				var chartDimensions = $telerik.getBounds(chart.get_element().parentElement);
				chart.set_width("'" + (chartDimensions.width / docDimensions.width) + "%'");
				chart.set_height(("'" + chartDimensions.height / docDimensions.height) + "'%");
			}

			var doit;
			window.onresize = function () {
				clearTimeout(doit);
				doit = setTimeout(resizedw, 1000);
			};
		</script>
		<table>
			<tr>
				<td>
					<telerik:RadHtmlChart runat="server" ID="DonutChart" Width="100%" Height="100%" Transitions="true">
						<Appearance>
							<FillStyle BackgroundColor="White"></FillStyle>
						</Appearance>
						<ChartTitle Text="OS Usage Statistics for December 2012">
							<Appearance Align="Center" Position="Top"></Appearance>
						</ChartTitle>
						<PlotArea>
							<Series>
								<telerik:DonutSeries>
									<LabelsAppearance Visible="false">
									</LabelsAppearance>
									<TooltipsAppearance DataFormatString="{0}%" BackgroundColor="White"></TooltipsAppearance>
									<SeriesItems>
										<telerik:PieSeriesItem BackgroundColor="#00adcc" Name="Win7"
											Y="55.6"></telerik:PieSeriesItem>
										<telerik:PieSeriesItem BackgroundColor="#cccccc" Name="Win8" Y="2.5"></telerik:PieSeriesItem>
										<telerik:PieSeriesItem BackgroundColor="#999999" Name="Vista" Y="2.8"></telerik:PieSeriesItem>
										<telerik:PieSeriesItem BackgroundColor="#888888" Name="NT" Y="1.8"></telerik:PieSeriesItem>
										<telerik:PieSeriesItem BackgroundColor="#777777" Name="WinXP" Y="21.1"></telerik:PieSeriesItem>
										<telerik:PieSeriesItem BackgroundColor="#666666" Name="Linux" Y="4.7"></telerik:PieSeriesItem>
										<telerik:PieSeriesItem BackgroundColor="#555555" Name="Mac" Y="8.7"></telerik:PieSeriesItem>
										<telerik:PieSeriesItem BackgroundColor="#444444" Name="Mobile" Y="2.2"></telerik:PieSeriesItem>
									</SeriesItems>
								</telerik:DonutSeries>
							</Series>
						</PlotArea>
					</telerik:RadHtmlChart>
				</td>
				<td>
					<telerik:RadHtmlChart runat="server" ID="RadarAreaChart" Width="100%" Height="100%" Transitions="true">
						<PlotArea>
							<Series>
								<telerik:RadarAreaSeries Name="Position" MissingValues="Gap">
									<Appearance>
										<FillStyle BackgroundColor="#00adcc"></FillStyle>
									</Appearance>
									<LineAppearance Width="1" />
									<MarkersAppearance Visible="false" />
									<LabelsAppearance Visible="false"></LabelsAppearance>
									<SeriesItems>
										<telerik:CategorySeriesItem Y="159"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="170"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="100"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="140"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="160"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="103"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="173"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="107"></telerik:CategorySeriesItem>
									</SeriesItems>
								</telerik:RadarAreaSeries>
								<telerik:RadarAreaSeries Name="Person" MissingValues="Gap">
									<Appearance>
										<FillStyle BackgroundColor="red"></FillStyle>
									</Appearance>
									<LabelsAppearance Visible="false">
									</LabelsAppearance>
									<LineAppearance Width="1" />
									<MarkersAppearance Visible="false"></MarkersAppearance>
									<SeriesItems>
										<telerik:CategorySeriesItem Y="130"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="160"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="130"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="168"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="150"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="140"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="109"></telerik:CategorySeriesItem>
										<telerik:CategorySeriesItem Y="76"></telerik:CategorySeriesItem>
									</SeriesItems>
								</telerik:RadarAreaSeries>
							</Series>
							<XAxis Color="Black" Reversed="false" StartAngle="180">
								<MajorGridLines Color="#EFEFEF" Width="1"></MajorGridLines>
								<MinorGridLines Visible="false"></MinorGridLines>
								<Items>
									<telerik:AxisItem LabelText="Soft Skills"></telerik:AxisItem>
									<telerik:AxisItem LabelText="Sector knowledge"></telerik:AxisItem>
									<telerik:AxisItem LabelText="Finance knowledge"></telerik:AxisItem>
									<telerik:AxisItem LabelText="Work experience"></telerik:AxisItem>
									<telerik:AxisItem LabelText="Win7 skills"></telerik:AxisItem>
									<telerik:AxisItem LabelText="MS Office skills"></telerik:AxisItem>
									<telerik:AxisItem LabelText="Programming skills"></telerik:AxisItem>
									<telerik:AxisItem LabelText="Database skills"></telerik:AxisItem>
								</Items>
							</XAxis>
							<YAxis Visible="false">
								<MajorGridLines Color="#EFEFEF" Width="1"></MajorGridLines>
								<MinorGridLines Visible="false"></MinorGridLines>
								<LabelsAppearance Step="1"></LabelsAppearance>
							</YAxis>
							<CommonTooltipsAppearance Color="White"></CommonTooltipsAppearance>
						</PlotArea>
						<ChartTitle Text="Position Profile">
							<Appearance Align="Center" BackgroundColor="White" Position="Top">
							</Appearance>
						</ChartTitle>
						<Legend>
							<Appearance BackgroundColor="White" Position="Bottom">
							</Appearance>
						</Legend>
					</telerik:RadHtmlChart>
				</td>
			</tr>
		</table>
	</form>

The chart's labels also look misaligned in rtl direction, so you can change only chart's direction to ltr with CSS:
	<style>
		.RadHtmlChart {
			direction: ltr;
		}
	</style>

		<div dir="rtl">
			some text
		<telerik:RadHtmlChart ID="RadHtmlChart1" runat="server" Width="600" Height="400">
			<PlotArea>
				<Series>
					<telerik:ColumnSeries Name="Series 1">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="30" />
							<telerik:CategorySeriesItem Y="10" />
							<telerik:CategorySeriesItem Y="20" />
						</SeriesItems>
					</telerik:ColumnSeries>
				</Series>
				<XAxis>
					<LabelsAppearance RotationAngle="33"></LabelsAppearance>
					<Items>
						<telerik:AxisItem LabelText="Item 1" />
						<telerik:AxisItem LabelText="Item 2" />
						<telerik:AxisItem LabelText="Item 3" />
					</Items>
				</XAxis>
			</PlotArea>
		</telerik:RadHtmlChart>
		</div>

allow for the chart plot area to be fixed width not counting the axis text. the issue I have is the legend on right side of chart changes the widths of chart when the text is long.

export of the chart to image (or pdf) will show an html code of non-breaking space in chart title and chart legend, but not in a label added to HtmlChartHolder

A visual example - http://i.stack.imgur.com/zRwlo.jpg

The feature will be useful for projects that need 508 compliance.

A boolean properties will also be useful: "EnabledTexturedFill", "EnableColorAndTexturedFill"

I have a column series chart.
I have set colorfield for each series.
Series background change correctly, but label color does not change as per series color.
I can not set label color dynamically.

The selection (http://demos.telerik.com/kendo-ui/chart-api/selection) can be configured through the kendo widget:
		<script>
			function pageLoad(args) {
				var kendoWidget = $find("<%=RadHtmlChart1.ClientID%>").get_kendoWidget();
				kendoWidget.options.categoryAxis.select = { from: 1, to: 2 };
				kendoWidget.bind("selectStart", onSelectStart);
				kendoWidget.bind("select", onSelect);
				kendoWidget.bind("selectEnd", onSelectEnd);

				kendoWidget.redraw();
			}

			function formatRange(e) {
				var categories = e.axis.categories;

				return kendo.format("{0} - {1} ({2} - {3})",
					e.from, e.to,
					categories[e.from],
					// The last category included in the selection is at (to - 1)
					categories[e.to - 1]
				);
			}

			function onSelectStart(e) {
				console.log(kendo.format("Select start :: {0}", formatRange(e)));
			}

			function onSelect(e) {
				console.log(kendo.format("Select :: {0}", formatRange(e)));
			}

			function onSelectEnd(e) {
				console.log(kendo.format("Select end :: {0}", formatRange(e)));
			}
		</script>
		<telerik:RadHtmlChart runat="server" ID="RadHtmlChart1" Width="600px" Height="400px">
			<PlotArea>
				<Series>
					<telerik:ColumnSeries Name="Product 1">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="1" />
							<telerik:CategorySeriesItem Y="2" />
							<telerik:CategorySeriesItem Y="3" />
							<telerik:CategorySeriesItem Y="4" />
							<telerik:CategorySeriesItem Y="2" />
						</SeriesItems>
					</telerik:ColumnSeries>
				</Series>
				<XAxis>
					<Items>
						<telerik:AxisItem LabelText="1" />
						<telerik:AxisItem LabelText="2" />
						<telerik:AxisItem LabelText="3" />
						<telerik:AxisItem LabelText="4" />
						<telerik:AxisItem LabelText="5" />
					</Items>
				</XAxis>
			</PlotArea>
		</telerik:RadHtmlChart>

I would like to suggest ability to display data series in doughnut and pie charts, see attached example from Excel.

And thanks for a great Telerik experience, you make my development work very easy.

If our X-axis is filled by numeric values, we don't want to navigate by date or by category or by logaritmic. We may want those values, the same shown in X-axis, determinating our chart.
For instance: latitude (X-axis) and longitude (Y-axis). We want to navigate by latitude and select view from lat. = 44 to lat. = 45. Date or datetime would be meaningless.
Will it be possible?

For the time being you can use a JavaScript function inside the template to cut the labels - http://docs.telerik.com/kendo-ui/dataviz/chart/how-to/shorten-chart-labels

Hello,

The RadHtmlCharts are great! One that is missing however -- a spectrum chart, aka a spectral chart. This takes in a set of data points and renders the values as color-dense shadings. Screenshot attached of one we made ourselves.

This would be useful for scientific applications.


thanks,
matt

Reproduction steps - Run the code below and click Show Chart - chart is not displayed.
ASPX:
		<div id="div1" style="visibility: hidden;">
			<telerik:RadHtmlChart runat="server" ID="ColumnChart1" Width="600px" Height="400px">
				<PlotArea>
					<Series>
						<telerik:ColumnSeries Name="Product 1">
							<SeriesItems>
								<telerik:CategorySeriesItem Y="1" />
								<telerik:CategorySeriesItem Y="2" />
								<telerik:CategorySeriesItem Y="3" />
							</SeriesItems>
						</telerik:ColumnSeries>
					</Series>
				</PlotArea>
			</telerik:RadHtmlChart>
		</div>
		<div id="chart" style="visibility: hidden;">HtmlChart wrapper</div>
		<input type="button" onclick="showChart(); return false;" value="Show Chart" />
		<script>
			$ = $telerik.$;
			function showChart() {
				$("#div1").attr("style", "visibility:visible");
			}
		</script>
Solution 1:
Use the workaround below:
		<telerik:RadRotator ID="RadRotator1" runat="server" Height="500px" ItemHeight="300px" ItemWidth="300px" Skin="Default" Width="1000px" RotatorType="AutomaticAdvance">
			<Items>
				<telerik:RadRotatorItem>
					<ItemTemplate>
						<telerik:RadHtmlChart ID="RadHtmlChart2" runat="server" Height="300px" Skin="Silk" Width="300px" Transitions="False" Visible="true">
							<PlotArea>
								<Series>
									<telerik:PieSeries>
										<SeriesItems>
											<telerik:PieSeriesItem Name="a" Y="12" />
											<telerik:PieSeriesItem Name="b" Y="5" />
										</SeriesItems>
									</telerik:PieSeries>
								</Series>
							</PlotArea>
						</telerik:RadHtmlChart>
					</ItemTemplate>
				</telerik:RadRotatorItem>
			</Items>
			<ItemTemplate>
			</ItemTemplate>
		</telerik:RadRotator>
		<script>
			$ = $telerik.$;
			Telerik.Web.UI.RadHtmlChart.prototype.repaint = function () {
				var that = this;
				if (that._chartObject) {
					if (that._isDataSourceChanged()) {
						that._loadData();
					}
					else {
						that._resetVisibilityOption();
						that._chartObject.redraw();
					}
				}
			};

			Telerik.Web.UI.RadHtmlChart.prototype._resetVisibilityOption = function () {
				var that = this;
				that._chartObject.options.visible = that._options.visible = that.get_visible();
			};

			Telerik.Web.UI.RadHtmlChart.prototype._getMainConfig = function () {
				var that = this;
				//when visible is false - nothing is sent from the server to save transferred data
				//e.g - there are properties set but visible is false - we do not need to send those properties amyway
				//that is why - set visible: false when nothing is sent from the server
				that._options = $telerik._getPropertiesParameter(that, that.constructor);
				that._cleanUpConfigProperties();

				that._options["theme"] = that.get_skin();
				that._options["visible"] = $(that.get_element()).is(':visible');
				that._options["title"] = that._chartTitle ? that._parseObject(that._chartTitle) : { visible: false };
				that._options["legend"] = that._legend ? that._parseObject(that._legend) : { visible: false };

				if (that._chartArea) {
					that._options["chartArea"] = that._parseObject(that._chartArea);
				}

				if (that._isSparklineChart()) {
					that._setMinimumSparklineWidth();
				}

				if (that._plotArea) {
					that._configurePlotArea();
				}

				if (that._series) {
					/*jshint evil: true */
					that._options["series"] = eval(that._series);
					/*jshint evil: false */
				}

				if (that._isStockChart()) {
					that._configureStockChart();
				}
			};
		</script>
Solution 2:
Hide the chart on load event:
		<div id="div1">
			<telerik:RadHtmlChart runat="server" ID="ColumnChart1" Width="600px" Height="400px">
				<ClientEvents OnLoad="OnLoad" />
				<PlotArea>
					<Series>
						<telerik:ColumnSeries Name="Product 1">
							<SeriesItems>
								<telerik:CategorySeriesItem Y="1" />
								<telerik:CategorySeriesItem Y="2" />
								<telerik:CategorySeriesItem Y="3" />
							</SeriesItems>
						</telerik:ColumnSeries>
					</Series>
				</PlotArea>
			</telerik:RadHtmlChart>
		</div>
		<div id="chart" style="visibility: hidden;">HtmlChart wrapper</div>
		<input type="button" onclick="showChart(); return false;" value="Show Chart" />
		<script>
			$ = $telerik.$;
			function showChart() {
				$("#div1").attr("style", "visibility:visible");
			}

			function OnLoad() {
				$("#div1").attr("style", "visibility:hidden");
			}

		</script>

For the time being the property can be set through the kendo widget:
		<script type="text/javascript">
			function pageLoad() {
				var kendoWidget = $find("<%=RadHtmlChart1.ClientID%>").get_kendoWidget();
				kendoWidget.options.series[0].color = function (e) {
					if (e.value > 20) {
						return "red";
					}
					else {
						return "green";
					}
				}
				kendoWidget.redraw();
			}
		</script>
		<telerik:RadHtmlChart ID="RadHtmlChart1" runat="server" Width="600" Height="400">
			<PlotArea>
				<Series>
					<telerik:ColumnSeries>
						<SeriesItems>
							<telerik:CategorySeriesItem Y="30" />
							<telerik:CategorySeriesItem Y="10" />
							<telerik:CategorySeriesItem Y="20" />
						</SeriesItems>
					</telerik:ColumnSeries>
				</Series>
			</PlotArea>
		</telerik:RadHtmlChart>

For the time being you can manually fetch the data and pass it to the chart:
		<script>
			function pageLoad() {
				var dataSource = $find('<%= RadClientDataSource1.ClientID %>');
				dataSource.fetch(function (args) {
					var data = args.get_data(),
						chart = $find('<%=RadHtmlChart1.ClientID%>');
					//workaround
					chart.set_dataSource(data);
					chart.repaint();
				});
			}
		</script>
		<telerik:RadClientDataSource ID="RadClientDataSource1" runat="server">
			<DataSource>
				<WebServiceDataSourceSettings>
					<Select Url="spain-electricity.json" DataType="JSON" />
				</WebServiceDataSourceSettings>
			</DataSource>
			<Schema>
				<Model>
					<telerik:ClientDataSourceModelField FieldName="year" DataType="String" />
					<telerik:ClientDataSourceModelField FieldName="solar" DataType="Number" />
				</Model>
			</Schema>
		</telerik:RadClientDataSource>

		<telerik:RadHtmlChart ID="RadHtmlChart1" runat="server" ClientDataSourceID="RadClientDataSource1">
			<PlotArea>
				<Series>
					<telerik:LineSeries DataFieldY="year" Name="year">
					</telerik:LineSeries>
				</Series>
				<XAxis DataLabelsField="year"></XAxis>
			</PlotArea>
		</telerik:RadHtmlChart>

For the time being the function can be set through the kendoWidget:

<telerik:RadHtmlChart runat="server" ID="ColumnChart1" Transitions="true">
    <PlotArea>
        <Series>
            <telerik:ColumnSeries Name="Product 1">
                <TooltipsAppearance BackgroundColor="Orange" DataFormatString="{0} sales" />
                <SeriesItems>
                    <telerik:CategorySeriesItem Y="15000" />
                    <telerik:CategorySeriesItem Y="23000" />
                    <telerik:CategorySeriesItem Y="10000" />
                    <telerik:CategorySeriesItem Y="16000" />
                </SeriesItems>
            </telerik:ColumnSeries>
        </Series>
        <XAxis AxisCrossingValue="0" Color="Black" MajorTickType="Outside" MinorTickType="Outside"
            Reversed="false">
            <Items>
                <telerik:AxisItem LabelText="1" />
                <telerik:AxisItem LabelText="2" />
                <telerik:AxisItem LabelText="3" />
                <telerik:AxisItem LabelText="4" />
            </Items>
            <LabelsAppearance DataFormatString="Q{0}" RotationAngle="0" />
            <MajorGridLines Color="#EFEFEF" Width="1" />
            <MinorGridLines Color="#F7F7F7" Width="1" />
            <TitleAppearance Position="Center" RotationAngle="0" Text="Quarters" />
        </XAxis>
        <YAxis AxisCrossingValue="0" Color="Black" MajorTickSize="1" MajorTickType="Outside"
            MaxValue="50000" MinorTickSize="1" MinorTickType="Outside" MinValue="0" Reversed="false"
            Step="10000">
            <LabelsAppearance DataFormatString="{0} sales" RotationAngle="0" />
            <TitleAppearance Position="Center" RotationAngle="0" Text="Sales" />
        </YAxis>
    </PlotArea>
    <ChartTitle Text="Product Sales for 2011">
    </ChartTitle>
    <Legend>
        <Appearance Position="Bottom" />
    </Legend>
</telerik:RadHtmlChart>
<script>
    function pageLoad() {
        $ = $telerik.$;
        var kendoWidget = $find("<%=ColumnChart1.ClientID%>").get_kendoWidget();
        kendoWidget.options.series[0].labels.position = function (point) {
            if (point.value < 20000) {
                console.log(1);
                return "insideEnd";
            } else {
                console.log(2);
                return "outsideEnd";
            }
        }
        kendoWidget.redraw();
    }
</script>

The property (http://docs.telerik.com/kendo-ui/api/javascript/dataviz/ui/chart#configuration-categoryAxis.maxDateGroups) can be set through the kendoWidget:
JavaScript:

        <script>
            function OnLoad(args) {
                var kendoWidget = args.get_kendoWidget();
                kendoWidget.options.categoryAxis.maxDateGroups = 8;
                kendoWidget.options.categoryAxis.baseUnit = 'fit';
                kendoWidget.redraw();
            }
        </script>

ASPX:

        <telerik:RadHtmlChart runat="server" ID="RadHtmlChart2" Width="640px" Height="480px">
            <ClientEvents OnLoad="OnLoad" />
            <PlotArea>
                <Series>
                    <telerik:LineSeries DataFieldY="SellQuantity">
                        <LabelsAppearance DataFormatString="{1} cars sold on {0:m}">
                        </LabelsAppearance>
                        <TooltipsAppearance Color="White" DataFormatString="{1} cars sold on<br/>{0:D}" />
                    </telerik:LineSeries>
                </Series>
                <XAxis DataLabelsField="SellDate">
                    <TitleAppearance Text="Sell Date">
                    </TitleAppearance>
                    <LabelsAppearance DataFormatString="d">
                    </LabelsAppearance>
                    <MajorGridLines Color="#EFEFEF" Width="1"></MajorGridLines>
                    <MinorGridLines Color="#F7F7F7" Width="1"></MinorGridLines>
                </XAxis>
                <YAxis>
                    <TitleAppearance Text="Quantity">
                    </TitleAppearance>
                    <MajorGridLines Color="#EFEFEF" Width="1"></MajorGridLines>
                    <MinorGridLines Color="#F7F7F7" Width="1"></MinorGridLines>
                </YAxis>
            </PlotArea>
            <ChartTitle Text="Sold Cars per Date">
            </ChartTitle>
        </telerik:RadHtmlChart>

C#:

    protected void Page_Load(object sender, EventArgs e)
    {
        RadHtmlChart2.DataSource = GetData();
        RadHtmlChart2.DataBind();
    }

    protected DataTable GetData()
    {
        DataTable dt = new DataTable();

        dt.Columns.Add("ID", typeof(int));
        dt.Columns.Add("SellQuantity", typeof(int));
        dt.Columns.Add("SellDate", typeof(DateTime));

        dt.Rows.Add(1, 2, new DateTime(2011, 06, 12));
        dt.Rows.Add(2, 5, new DateTime(2011, 12, 12));
        dt.Rows.Add(3, 6, new DateTime(2012, 06, 17));
        dt.Rows.Add(4, 4, new DateTime(2012, 09, 18));
        dt.Rows.Add(5, 7, new DateTime(2013, 03, 18));

        return dt;
    }