How much data / information can we save / store in a QR code?

QR codes have three parameters: Datatype, size (number of 'pixels') and error correction level. How much information can be stored there also depends on these parameters. For example the lower the error correction level, the more information that can be stored, but the harder the code is to recognize for readers.

The maximum size and the lowest error correction give the following values:
Numeric only Max. 7,089 characters
Alphanumeric Max. 4,296 characters
Binary/byte Max. 2,953 characters (8-bit bytes)

See this table.

A 101x101 QR code, with high level error correction, can hold 3248 bits, or 406 bytes. Probably not enough for any meaningful SVG/XML data.

A 177x177 grid, depending on desired level of error correction, can store between 1273 and 2953 bytes. Maybe enough to store something small.