# XML and SVG


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## Elements

``` apl
]help •element
```

`•element tag` returns an element function for XML tag `tag`. Call it
with attributes on the left and children on the right, as in
`('r':10) circle ''`. An empty right argument, `''` or `⍬`, gives no
children. It returns a keyed vector with `tag`, `attrs` and `children`
entries.

Errors: DOMAIN for invalid tag or attribute names.

Here `text` makes `text` elements. The result is an ordinary keyed
vector:

``` apl
text←•element 'text'
label←('x':10 ⋄ 'y':20) text 'a < b'
label
```

    ('tag':'text' ⋄ 'attrs':('x':10 ⋄ 'y':20) ⋄ 'children':'a < b')

## XML

``` apl
]help •xml
```

`•xml tree` returns the XML text of an element tree. It escapes `&`,
`<`, `>` and `"` in text and attribute values. A numeric vector
attribute becomes space-separated numbers. Children are text, elements
or vectors of children. An element with no children closes itself.

Errors: DOMAIN for invalid names or attribute values.

`•xml` escapes text:

``` apl
•xml label
```

    <text x="10" y="20">a &lt; b</text>

A numeric vector attribute becomes space-separated numbers. An element
with no children closes itself. `''` and `⍬` both mean no children:

``` apl
g←•element 'g'
•xml ('fill':'red' ⋄ 'points':1 2 3 4) g ⍬
```

    <g fill="red" points="1 2 3 4"/>

Children can be a vector of elements:

``` apl
•xml g (text 'a') (text 'b')
```

    <g><text>a</text><text>b</text></g>

Attribute names keep their case. Prefixed names such as `xlink:href`
pass through unchanged.

## SVG

``` apl
]help •svg
```

`X •svg children` returns an `svg` element with attributes `X`. It adds
`xmlns` for the SVG namespace and `viewBox="0 0 100 100"`. Attributes in
`X` replace these. Its `_mime_` field makes notebooks display it as a
picture.

`width` and `height` set the picture’s displayed size:

``` apl
circle←•element 'circle'
c←('cx':50 ⋄ 'cy':40 ⋄ 'r':25 ⋄ 'fill':'orange') circle ''
t←('x':50 ⋄ 'y':85 ⋄ 'text-anchor':'middle') text 'Hello'
pic←('width':240 ⋄ 'height':240) •svg (c ⋄ t)
pic
```

![](xml_files/figure-commonmark/cell-9-output-1.svg)

Elements are keyed arrays with `tag`, `attrs` and `children` entries.
Edit them using ordinary assignment. Display serializes the current
tree.

``` apl
pic.children[1].attrs.fill←'steelblue'
pic
```

![](xml_files/figure-commonmark/cell-10-output-1.svg)

Override `viewBox` with four numbers to choose the drawing coordinates.

``` apl
('viewBox':0 0 200 100 ⋄ 'width':400 ⋄ 'height':200) •svg pic.children
```

![](xml_files/figure-commonmark/cell-11-output-1.svg)

## Rich display

``` apl
]help •mime
```

`•mime Y` returns the MIME bundle that display uses for `Y`. The bundle
is a keyed vector from MIME types to text. It always has `text/plain`.
If `Y` has a function in its `_mime_` field, `•mime` calls it with `Y`
as `⍵` and adds its entries.

Display shows the text form when a renderer fails. Only a direct `•mime`
call reports the error.

Any keyed vector with a function in its `_mime_` field displays through
that function. The function receives the keyed vector as `⍵` and returns
a MIME-keyed array. Here the renderer displays the sum of `items`.

``` apl
total←('items':1 2 3)
total._mime_←{('text/plain':⍕+/⍵.items)}
total
```

    6

`_mime_` is an ordinary field. Edits keep it. The renderer sees the
current values.

``` apl
total.items+←10
total
```

    36

`•mime` shows the bundle that display uses:

``` apl
•mime total
```

    ('text/plain':'36')

Python arrays implement `_repr_mimebundle_()`. `apl(code, 'repl')`
captures ordered events in `Result.events`. `Result.output` extracts
their text. `⎕←` produces explicit text output. The native kernel,
notebook magics and `bapl-nb --save` use the rich bundles.