Property Files define properties. Properties are stored in key/value pairs and may only contain plain text. The suffix of these files should be .properties, the default Property File for a Build File is build.properties

# Property files contain key/value pairs
key=value

# Property keys may contain alphanumeric chars and colons, but
# not special chars. This way you can create pseudo-namespaces
myapp.window.hsize=300
myapp.window.vsize=200
myapp.window.xpos=10
myapp.window.ypos=100

# You can refer to values of other properties by enclosing their
# keys in "${}".
text.width=${myapp.window.hsize}

# Everything behind the equal sign is the value, you do
# not have to enclose strings:
text=This is some text, Your OS is ${php.os}

Property files may also be formatted in YAML format:

# Property files contain key/value pairs
key: value

# Nested values will be available as concatenated strings after import. E.g.,
# you may access these values with keys in the form of "myapp.window.hsize".
myapp:
  window:
     hsize: 300
     vsize: 200
     xpos: 10
     ypos: 100

# You can refer to values of other properties by enclosing their
# keys in "${}".
text:
  width: "${myapp.window.hsize}"

Property files may also be formatted in XML format:

<myapp>
    <window>
        <hsize>300</hsize>
        <vsize>200</hsize>
        <xpos>10</hsize>
        <ypos>100</hsize>
    </window>
</myapp>

myapp.window.hsize=300
myapp.window.vsize=200
myapp.window.xpos=10
myapp.window.ypos=100