In Section 20.43 chart:regression-type add the following item to the list (sub- and superscript seems to not work properly, but I think, you know to write a polynomial in x of degree n):

- polynomial - Polynomial regression - approximate the values of the series using the model: y = A~0~ + A~1~ x + A~2~ x^2^ + ... + A~n~ x^n^ where n is given by the
`chart:regression-max-degree` attribute.

The generated attribute list changes to:

The values of the `chart:regression-type` attribute are `none`, `linear`, `logarithmic`, `exponential`, `power` and `polynomial`.

Add these new sections in chapter 20

**chart:regression-max-degree**

The `chart:regression-max-degree` attribute specifies the maximum degree of a polynomial regression curve. This attribute is only evaluated together with attribute `chart:regression-type` and if that has the value `polynomial`.

The value of the `chart:regression-max-degree` attribute must be greater than or equal to 2.

The default value for this attribute is 2.

The generated text is then:

The `chart:regression-max-degree` attribute is usable with the following element: <style:chart-properties> 17.22.

The `chart:regression-max-degree` attribute has the data type `positiveInteger`.

**chart:regression-force-intercept**

The `chart:regression-force-intercept` attribute specifies whether a regression curve of type `linear`, `exponential` or `polynomial` must intercept the y-axis at a certain value.

The defined values for the `chart:regression-force-intercept` attribute are:

• `true`: The regression curve intercepts the y‑axis at the value, which is defined by the `chart:regression-intercept-value` attribute.

• `false`: The interception of regression-curve and y-axis is calculated from the data series.

The default value for this attribute is `false`.

This attribute is only evaluated together with attribute `chart:regression-type` and if that has one of the following values: `linear`, `exponential` or `polynomial`.

The generated text is then:

The `chart:regression-force-intercept` attribute is usable with the following element: `<style:chart-properties>` 17.22.

The `chart:regression-force-intercept` attribute has the data type `boolean`.

**chart:regression-intercept-value**

The `chart:regression-intercept-value` attribute specifies where a regression curve must intercept the y-axis, if attribute `chart:regression-force-intercept` is `true`.

This attribute is only evaluated together with `chart:regression-force-intercept` attribute.

The default value for this attribute is 0 in case of regression type `linear` or `polynomial`, and the default value is 1 in case of regression type `exponential`.

The generated text is then:

The `chart:regression-intercept-value` attribute is usable with the following element: `<style:chart-properties>` 17.22.

The `chart:regression-intercept-value` attribute has the data type `double`.

**chart:regression-name**

The `chart:regression-name` attribute specifies a name of a regression curve.

Default value is an empty string.

The generated text is then:

The `chart:regression-name` attribute is usable with the following element: `<style:chart-properties>` 17.22.

The `chart:regression-name` attribute has the data type `string`.

The needed change to the schema is given by this diff:

--- OpenDocument-schema-v1.3_ohneTab.rng 2018-06-06 00:01:34.171094900 +0200
+++ OpenDocument-schema-v1.3_regression_curve1.rng 2018-06-05 23:59:49.276136600 +0200
@@ -9993,14 +9993,35 @@
<rng:value>none</rng:value>
<rng:value>linear</rng:value>
<rng:value>logarithmic</rng:value>
<rng:value>exponential</rng:value>
<rng:value>power</rng:value>
+ <rng:value>polynomial</rng:value>
</rng:choice>
</rng:attribute>
</rng:optional>
<rng:optional>
+ <rng:attribute name="chart:regression-max-degree">
+ <rng:ref name="positiveInteger"/>
+ </rng:attribute>
+ </rng:optional>
+ <rng:optional>
+ <rng:attribute name="chart:regression-force-intercept">
+ <rng:ref name="boolean"/>
+ </rng:attribute>
+ </rng:optional>
+ <rng:optional>
+ <rng:attribute name="chart:regression-intercept-value">
+ <rng:ref name="double"/>
+ </rng:attribute>
+ </rng:optional>
+ <rng:optional>
+ <rng:attribute name="chart:regression-name">
+ <rng:ref name="string"/>
+ </rng:attribute>
+ </rng:optional>
+ <rng:optional>
<rng:attribute name="chart:axis-position">
<rng:choice>
<rng:value>start</rng:value>
<rng:value>end</rng:value>
<rng:ref name="double"/>