multiple <figcaption> elements must not be placed within <figure> element

[mtrootyy]

When multiple <figcaption> elements are placed within <figure> element, "The W3C Markup Validation Service" output an error.
But this thing is not clearly stipulated in HTML5.3 specification.

Therefore, two fixes are necessary.

https://w3c.github.io/html/grouping-content.html#the-figure-element

Content model:

• Flow content optionally including a figcaption child element.

↓
The above should be fixed following;

Content model:

• Flow content optionally including only one figcaption child element.

https://w3c.github.io/html/grouping-content.html#the-figcaption-element

Contexts in which this element can be used:

• As a child of a figure element.

↓
The above should be fixed following;

Contexts in which this element can be used:

• As a child of a figure element, but with no other figcaption elements within the figure element.

[mtrootyy]

At the same time, the following should be fixed.

https://w3c.github.io/html/grouping-content.html#the-figure-element

The figcaption descendant of figure, if any, represents the caption of the figure element’s contents. If there is no child figcaption element, then there is no caption.

↓
The above should be fixed following;

The figcaption child of figure, if any, represents the caption of the figure element’s contents. If there is no child figcaption element, then there is no caption.