diff --git a/demos/modules/demo_chart.mjs b/demos/modules/demo_chart.mjs
index 65133412b..5bb208d26 100644
--- a/demos/modules/demo_chart.mjs
+++ b/demos/modules/demo_chart.mjs
@@ -3,8 +3,8 @@
  * AUTH: Brent Ely (https://github.com/gitbrent/)
  * DESC: Common test/demo slides for all library features
  * DEPS: Used by various demos (./demos/browser, ./demos/node, etc.)
- * VER.: 3.11.0
- * BLD.: 20220806
+ * VER.: 3.12.0
+ * BLD.: 20230116
  */
 
 import { BASE_TABLE_OPTS, BASE_TEXT_OPTS_L, BASE_TEXT_OPTS_R, FOOTER_TEXT_OPTS, IMAGE_PATHS, TESTMODE } from "./enums.mjs";
@@ -901,8 +901,8 @@ function genSlide07(pptx) {
 			valAxisMaxVal: 1,
 			barDir: "bar",
 			axisLabelFormatCode: "#%",
-			catGridLine: { color: "D8D8D8", style: "dash", size: 1 },
-			valGridLine: { color: "D8D8D8", style: "dash", size: 1 },
+			catGridLine: { color: "D8D8D8", style: "dash", size: 1, cap: "round" },
+			valGridLine: { color: "D8D8D8", style: "dash", size: 1, cap: "square" },
 			catAxisLineShow: false,
 			valAxisLineShow: false,
 			barGrouping: "stacked",
@@ -1029,6 +1029,7 @@ function genSlide10(pptx) {
 			y: idx < 3 ? 0.5 : idx < 6 ? 2.85 : 5.1,
 			w: 4.25,
 			h: 2.25,
+			lineCap: 'round',
 			lineDataSymbol: opt,
 			lineDataSymbolSize: idx == 5 ? 9 : idx == 6 ? 12 : null,
 			chartColors: COLORS_VIVID,
diff --git a/src/core-enums.ts b/src/core-enums.ts
index 83c76b864..81abd4bb5 100644
--- a/src/core-enums.ts
+++ b/src/core-enums.ts
@@ -18,7 +18,7 @@ export const DEF_CELL_BORDER: BorderProps = { type: 'solid', color: '666666', pt
 export const DEF_CELL_MARGIN_PT: [number, number, number, number] = [3, 3, 3, 3] // TRBL-style // DEPRECATED 3.8.0
 export const DEF_CELL_MARGIN_IN: [number, number, number, number] = [0.05, 0.1, 0.05, 0.1] // "Normal" margins in PPT-2021 ("Narrow" is `0.05` for all 4)
 export const DEF_CHART_BORDER: BorderProps = { type: 'solid', color: '363636', pt: 1 }
-export const DEF_CHART_GRIDLINE: OptsChartGridLine = { color: '888888', style: 'solid', size: 1 }
+export const DEF_CHART_GRIDLINE: OptsChartGridLine = { color: '888888', style: 'solid', size: 1, cap: 'flat' }
 export const DEF_FONT_COLOR = '000000'
 export const DEF_FONT_SIZE = 12
 export const DEF_FONT_TITLE_SIZE = 18
diff --git a/src/core-interfaces.ts b/src/core-interfaces.ts
index 6c94425dd..bb05c2e10 100644
--- a/src/core-interfaces.ts
+++ b/src/core-interfaces.ts
@@ -1112,6 +1112,8 @@ export interface OptsDataLabelPosition {
 */
 
 export type ChartAxisTickMark = 'none' | 'inside' | 'outside' | 'cross'
+export type ChartLineCap = 'flat' | 'round' | 'square'
+
 export interface OptsChartData {
 	_dataIndex?: number
 
@@ -1147,6 +1149,12 @@ export interface IOptsChartData extends OptsChartData {
 	labels?: string[][]
 }
 export interface OptsChartGridLine {
+	/**
+	 * MS-PPT > Chart format > Format Major Gridlines > Line > Cap type
+	 * - line cap type
+	 * @default flat
+	 */
+	cap?: ChartLineCap
 	/**
 	 * Gridline color (hex)
 	 * @example 'FF3399'
@@ -1432,6 +1440,17 @@ export interface IChartPropsChartDoughnut {
 	holeSize?: number
 }
 export interface IChartPropsChartLine {
+	/**
+	 * MS-PPT > Chart format > Format Data Series > Line > Cap type
+	 * - line cap type
+	 * @default flat
+	 */
+	lineCap?: ChartLineCap
+	/**
+	 * MS-PPT > Chart format > Format Data Series > Marker Options > Built-in > Type
+	 * - line dash type
+	 * @default solid
+	 */
 	lineDash?: 'dash' | 'dashDot' | 'lgDash' | 'lgDashDot' | 'lgDashDotDot' | 'solid' | 'sysDash' | 'sysDot'
 	/**
 	 * MS-PPT > Chart format > Format Data Series > Marker Options > Built-in > Type
diff --git a/src/gen-charts.ts b/src/gen-charts.ts
index 6c81fe1a6..1785c89b7 100644
--- a/src/gen-charts.ts
+++ b/src/gen-charts.ts
@@ -19,8 +19,8 @@ import {
 	LETTERS,
 	ONEPT,
 } from './core-enums'
-import { IChartOptsLib, ISlideRelChart, ShadowProps, IChartPropsTitle, OptsChartGridLine, IOptsChartData } from './core-interfaces'
-import { createColorElement, genXmlColorSelection, convertRotationDegrees, encodeXmlEntities, getUuid, valToPts } from './gen-utils'
+import { IChartOptsLib, ISlideRelChart, ShadowProps, IChartPropsTitle, OptsChartGridLine, IOptsChartData, ChartLineCap } from './core-interfaces'
+import { createColorElement, genXmlColorSelection, convertRotationDegrees, encodeXmlEntities, getMix, getUuid, valToPts } from './gen-utils'
 import JSZip from 'jszip'
 
 /**
@@ -860,11 +860,11 @@ function makeChartType (chartType: CHART_NAME, data: IOptsChartData[], opts: ICh
 					if (opts.lineSize === 0) {
 						strXml += '<a:ln><a:noFill/></a:ln>'
 					} else {
-						strXml += `<a:ln w="${valToPts(opts.lineSize)}" cap="flat"><a:solidFill>${createColorElement(seriesColor)}</a:solidFill>`
+						strXml += `<a:ln w="${valToPts(opts.lineSize)}" cap="${createLineCap(opts.lineCap)}"><a:solidFill>${createColorElement(seriesColor)}</a:solidFill>`
 						strXml += '<a:prstDash val="' + (opts.lineDash || 'solid') + '"/><a:round/></a:ln>'
 					}
 				} else if (opts.dataBorder) {
-					strXml += `<a:ln w="${valToPts(opts.dataBorder.pt)}" cap="flat"><a:solidFill>${createColorElement(opts.dataBorder.color)}</a:solidFill><a:prstDash val="solid"/><a:round/></a:ln>`
+					strXml += `<a:ln w="${valToPts(opts.dataBorder.pt)}" cap="${createLineCap(opts.lineCap)}"><a:solidFill>${createColorElement(opts.dataBorder.color)}</a:solidFill><a:prstDash val="solid"/><a:round/></a:ln>`
 				}
 
 				strXml += createShadowElement(opts.shadow, DEF_SHAPE_SHADOW)
@@ -1082,7 +1082,7 @@ function makeChartType (chartType: CHART_NAME, data: IOptsChartData[], opts: ICh
 					if (opts.lineSize === 0) {
 						strXml += '<a:ln><a:noFill/></a:ln>'
 					} else {
-						strXml += `<a:ln w="${valToPts(opts.lineSize)}" cap="flat"><a:solidFill>${createColorElement(tmpSerColor)}</a:solidFill>`
+						strXml += `<a:ln w="${valToPts(opts.lineSize)}" cap="${createLineCap(opts.lineCap)}"><a:solidFill>${createColorElement(tmpSerColor)}</a:solidFill>`
 						strXml += `<a:prstDash val="${opts.lineDash || 'solid'}"/><a:round/></a:ln>`
 					}
 
@@ -2018,7 +2018,7 @@ function createShadowElement (options: ShadowProps, defaults: object): string {
 function createGridLineElement (glOpts: OptsChartGridLine): string {
 	let strXml = '<c:majorGridlines>'
 	strXml += ' <c:spPr>'
-	strXml += `  <a:ln w="${valToPts(glOpts.size || DEF_CHART_GRIDLINE.size)}" cap="flat">`
+	strXml += `  <a:ln w="${valToPts(glOpts.size || DEF_CHART_GRIDLINE.size)}" cap="${createLineCap(glOpts.cap || DEF_CHART_GRIDLINE.cap)}">`
 	strXml += '  <a:solidFill><a:srgbClr val="' + (glOpts.color || DEF_CHART_GRIDLINE.color) + '"/></a:solidFill>' // should accept scheme colors as implemented in [Pull #135]
 	strXml += '   <a:prstDash val="' + (glOpts.style || DEF_CHART_GRIDLINE.style) + '"/><a:round/>'
 	strXml += '  </a:ln>'
@@ -2027,3 +2027,16 @@ function createGridLineElement (glOpts: OptsChartGridLine): string {
 
 	return strXml
 }
+
+function createLineCap(lineCap: ChartLineCap): string {
+	if (!lineCap || lineCap === 'flat') {
+		return 'flat';
+	} else if (lineCap === 'square') {
+		return 'sq';
+	} else if (lineCap === 'round') {
+		return 'rnd';
+	} else {
+		const neverLineCap: never = lineCap;
+		throw new Error(`Invalid chart line cap: ${neverLineCap}`);
+	}
+}
diff --git a/src/gen-objects.ts b/src/gen-objects.ts
index 4dca3b988..56e2e5047 100644
--- a/src/gen-objects.ts
+++ b/src/gen-objects.ts
@@ -139,6 +139,10 @@ export function addChartDefinition (target: PresSlide, type: CHART_NAME | IChart
 			console.warn('Warning: chart.gridLine.style options: `solid`, `dash`, `dot`.')
 			delete glOpts.style
 		}
+		if (glOpts.cap && ['flat', 'square', 'round'].indexOf(glOpts.cap) < 0) {
+			console.warn('Warning: chart.gridLine.cap options: `flat`, `square`, `round`.')
+			delete glOpts.cap
+		}
 	}
 
 	const chartId = ++_chartCounter
diff --git a/src/pptxgen.ts b/src/pptxgen.ts
index ae92fc03d..7726eca3a 100644
--- a/src/pptxgen.ts
+++ b/src/pptxgen.ts
@@ -97,7 +97,7 @@ import * as genMedia from './gen-media'
 import * as genTable from './gen-tables'
 import * as genXml from './gen-xml'
 
-const VERSION = '3.12.0-beta-20230116-1801'
+const VERSION = '3.12.0-beta-20230122-1830'
 
 export default class PptxGenJS implements IPresentationProps {
 	// Property getters/setters
diff --git a/types/index.d.ts b/types/index.d.ts
index 3ac0b6546..3a1290be8 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -1,4 +1,4 @@
-// Type definitions for pptxgenjs 3.11.0
+// Type definitions for pptxgenjs 3.12.0
 // Project: https://gitbrent.github.io/PptxGenJS/
 // Definitions by: Brent Ely <https://github.com/gitbrent/>
 //                 Michael Beaumont <https://github.com/michaelbeaumont>
@@ -1081,80 +1081,80 @@ declare namespace PptxGenJS {
 		 * @default false
 		 */
 		bullet?:
-			| boolean
-			| {
-					/**
-					 * Bullet type
-					 * @default bullet
-					 */
-					type?: 'bullet' | 'number'
-					/**
-					 * Bullet character code (unicode)
-					 * @since v3.3.0
-					 * @example '25BA' // 'BLACK RIGHT-POINTING POINTER' (U+25BA)
-					 */
-					characterCode?: string
-					/**
-					 * Indentation (space between bullet and text) (points)
-					 * @since v3.3.0
-					 * @default 27 // DEF_BULLET_MARGIN
-					 * @example 10 // Indents text 10 points from bullet
-					 */
-					indent?: number
-					/**
-					 * Number type
-					 * @since v3.3.0
-					 * @example 'romanLcParenR' // roman numerals lower-case with paranthesis right
-					 */
-					numberType?:
-						| 'alphaLcParenBoth'
-						| 'alphaLcParenR'
-						| 'alphaLcPeriod'
-						| 'alphaUcParenBoth'
-						| 'alphaUcParenR'
-						| 'alphaUcPeriod'
-						| 'arabicParenBoth'
-						| 'arabicParenR'
-						| 'arabicPeriod'
-						| 'arabicPlain'
-						| 'romanLcParenBoth'
-						| 'romanLcParenR'
-						| 'romanLcPeriod'
-						| 'romanUcParenBoth'
-						| 'romanUcParenR'
-						| 'romanUcPeriod'
-					/**
-					 * Number bullets start at
-					 * @since v3.3.0
-					 * @default 1
-					 * @example 10 // numbered bullets start with 10
-					 */
-					numberStartAt?: number
+		| boolean
+		| {
+			/**
+			 * Bullet type
+			 * @default bullet
+			 */
+			type?: 'bullet' | 'number'
+			/**
+			 * Bullet character code (unicode)
+			 * @since v3.3.0
+			 * @example '25BA' // 'BLACK RIGHT-POINTING POINTER' (U+25BA)
+			 */
+			characterCode?: string
+			/**
+			 * Indentation (space between bullet and text) (points)
+			 * @since v3.3.0
+			 * @default 27 // DEF_BULLET_MARGIN
+			 * @example 10 // Indents text 10 points from bullet
+			 */
+			indent?: number
+			/**
+			 * Number type
+			 * @since v3.3.0
+			 * @example 'romanLcParenR' // roman numerals lower-case with paranthesis right
+			 */
+			numberType?:
+			| 'alphaLcParenBoth'
+			| 'alphaLcParenR'
+			| 'alphaLcPeriod'
+			| 'alphaUcParenBoth'
+			| 'alphaUcParenR'
+			| 'alphaUcPeriod'
+			| 'arabicParenBoth'
+			| 'arabicParenR'
+			| 'arabicPeriod'
+			| 'arabicPlain'
+			| 'romanLcParenBoth'
+			| 'romanLcParenR'
+			| 'romanLcPeriod'
+			| 'romanUcParenBoth'
+			| 'romanUcParenR'
+			| 'romanUcPeriod'
+			/**
+			 * Number bullets start at
+			 * @since v3.3.0
+			 * @default 1
+			 * @example 10 // numbered bullets start with 10
+			 */
+			numberStartAt?: number
 
-					// DEPRECATED
+			// DEPRECATED
 
-					/**
-					 * Bullet code (unicode)
-					 * @deprecated v3.3.0 - use `characterCode`
-					 */
-					code?: string
-					/**
-					 * Margin between bullet and text
-					 * @since v3.2.1
-					 * @deplrecated v3.3.0 - use `indent`
-					 */
-					marginPt?: number
-					/**
-					 * Number to start with (only applies to type:number)
-					 * @deprecated v3.3.0 - use `numberStartAt`
-					 */
-					startAt?: number
-					/**
-					 * Number type
-					 * @deprecated v3.3.0 - use `numberType`
-					 */
-					style?: string
-			  }
+			/**
+			 * Bullet code (unicode)
+			 * @deprecated v3.3.0 - use `characterCode`
+			 */
+			code?: string
+			/**
+			 * Margin between bullet and text
+			 * @since v3.2.1
+			 * @deplrecated v3.3.0 - use `indent`
+			 */
+			marginPt?: number
+			/**
+			 * Number to start with (only applies to type:number)
+			 * @deprecated v3.3.0 - use `numberStartAt`
+			 */
+			startAt?: number
+			/**
+			 * Number type
+			 * @deprecated v3.3.0 - use `numberType`
+			 */
+			style?: string
+		}
 		/**
 		 * Text color
 		 * - `HexColor` or `ThemeColor`
@@ -1216,23 +1216,23 @@ declare namespace PptxGenJS {
 		 */
 		underline?: {
 			style?:
-				| 'dash'
-				| 'dashHeavy'
-				| 'dashLong'
-				| 'dashLongHeavy'
-				| 'dbl'
-				| 'dotDash'
-				| 'dotDashHeave'
-				| 'dotDotDash'
-				| 'dotDotDashHeavy'
-				| 'dotted'
-				| 'dottedHeavy'
-				| 'heavy'
-				| 'none'
-				| 'sng'
-				| 'wavy'
-				| 'wavyDbl'
-				| 'wavyHeavy'
+			| 'dash'
+			| 'dashHeavy'
+			| 'dashLong'
+			| 'dashLongHeavy'
+			| 'dbl'
+			| 'dotDash'
+			| 'dotDashHeave'
+			| 'dotDotDash'
+			| 'dotDotDashHeavy'
+			| 'dotted'
+			| 'dottedHeavy'
+			| 'heavy'
+			| 'none'
+			| 'sng'
+			| 'wavy'
+			| 'wavyDbl'
+			| 'wavyHeavy'
 			color?: Color
 		}
 		/**
@@ -1901,6 +1901,8 @@ declare namespace PptxGenJS {
 	*/
 
 	export type ChartAxisTickMark = 'none' | 'inside' | 'outside' | 'cross'
+	export type ChartLineCap = 'flat' | 'round' | 'square'
+
 	export interface OptsChartData {
 		/**
 		 * category labels
@@ -1930,6 +1932,12 @@ declare namespace PptxGenJS {
 		//color?: string // TODO: WIP: (Pull #727)
 	}
 	export interface OptsChartGridLine {
+		/**
+		 * MS-PPT > Chart format > Format Major Gridlines > Line > Cap type
+		 * - line cap type
+		 * @default flat
+		 */
+		cap?: ChartLineCap
 		/**
 		 * Gridline color (hex)
 		 * @example 'FF3399'
@@ -2179,6 +2187,16 @@ declare namespace PptxGenJS {
 		holeSize?: number
 	}
 	export interface IChartPropsChartLine {
+		/**
+		 * MS-PPT > Chart format > Format Data Series > Line > Cap type
+		 * - line cap type
+		 * @default flat
+		 */
+		lineCap?: ChartLineCap
+		/**
+		 * Line dash type
+		 * @default solid
+		 */
 		lineDash?: 'dash' | 'dashDot' | 'lgDash' | 'lgDashDot' | 'lgDashDotDot' | 'solid' | 'sysDash' | 'sysDot'
 		/**
 		 * MS-PPT > Chart format > Format Data Series > Marker Options > Built-in > Type
@@ -2289,21 +2307,21 @@ declare namespace PptxGenJS {
 	}
 	export interface IChartOpts
 		extends IChartPropsAxisCat,
-			IChartPropsAxisSer,
-			IChartPropsAxisVal,
-			IChartPropsBase,
-			IChartPropsChartBar,
-			IChartPropsChartDoughnut,
-			IChartPropsChartLine,
-			IChartPropsChartPie,
-			IChartPropsChartRadar,
-			IChartPropsDataLabel,
-			IChartPropsDataTable,
-			IChartPropsLegend,
-			IChartPropsTitle,
-			ObjectNameProps,
-			OptsChartGridLine,
-			PositionProps {
+		IChartPropsAxisSer,
+		IChartPropsAxisVal,
+		IChartPropsBase,
+		IChartPropsChartBar,
+		IChartPropsChartDoughnut,
+		IChartPropsChartLine,
+		IChartPropsChartPie,
+		IChartPropsChartRadar,
+		IChartPropsDataLabel,
+		IChartPropsDataTable,
+		IChartPropsLegend,
+		IChartPropsTitle,
+		ObjectNameProps,
+		OptsChartGridLine,
+		PositionProps {
 		/**
 		 * Alt Text value ("How would you describe this object and its contents to someone who is blind?")
 		 * - PowerPoint: [right-click on a chart] > "Edit Alt Text..."
@@ -2393,15 +2411,15 @@ declare namespace PptxGenJS {
 			| { rect: {} }
 			| { text: TextProps }
 			| {
-					placeholder: {
-						options: PlaceholderProps
-						/**
-						 * Text to be shown in placeholder (shown until user focuses textbox or adds text)
-						 * - Leave blank to have powerpoint show default phrase (ex: "Click to add title")
-						 */
-						text?: string
-					}
-			  }
+				placeholder: {
+					options: PlaceholderProps
+					/**
+					 * Text to be shown in placeholder (shown until user focuses textbox or adds text)
+					 * - Leave blank to have powerpoint show default phrase (ex: "Click to add title")
+					 */
+					text?: string
+				}
+			}
 		)[]
 
 		/**